Upgrade suggestions

I use my turntable as a source for less than five percent of my listening, but I am contemplating an upgrade and looking for advice.
I listen to classical music. I currently have been using a Rega P5 table with a PS Audio phono stage. I have had the table for 5 years and have never upgraded from the Rega mm cartridge that it came with.
the rest of my system is an Ayre preamplifier, Parasound Power amp, and some Digital sources (Marantz 803 SACD, NAd DVD-A player both fed into a PS Audio Digital Link DAC). Speakers are B&W 803-D.
budget up to $3000.
That's a very nice vinyl rig, I would think every bit as good as the rest of your rig. Maybe a Sumiko Blackbird, or a Soundsmith Aida cartridge set up properly? Get a MintLP protractor to set up your arm.
Over the years I have owned a lot of turntables, cartridges and phono preamps, and based on my experience here's what I'd suggest -

First, you already have a very good turntable and arm. I wouldn't mess with replacing either if they still function properly. Instead, I would suggest doing the following - look for a good pre-owned phono preamp on audiogon - a good choice would be an EAR 834P. The 834P can handle most MM and MC cartridgesThen, I'd purchase a Nitty Gritty 1.5 record cleaner, which will do more to improve the sound of your records than any other tweak you can buy. Then I'd take the balance of the $3000, whatever is left, and buy a new cartridge fro Shelter, Clearaudio, or Grado -- you might call the good folks at Needledoctor, if you don't have a local dealer you like, and ask for suggestions.
Keep the Rega P5 and get a better cartridge.
I just bought a P5 and put a Benz Glider on it.
So blow $900 on a cartridge (plenty of others in the 1K range, also get the P5 speed regulator, then spend a bunch on a used Phono section here.
That is if you only want to upgrade the LP playing. (which is not quite clear in your post)'But is you want other non-LP stuff, still get the new cart, $700 to $1000 area.
Or simply spend $500 on a mint used $1500 cartridge. I've done it here more than once. The last one I acquired, a Benz wood SH scoped out as a new cartridge would...the stylus showed zero wear. Your table is fine, now it's time to deck it out with a better stylus...there are a ton of nice used cartridges always for sale on AG. Buy one from a reputable seller. Better to make one change at a time so you can hear the differences you're making in the system. You can always upgrade or change electronics at a later time...baby steps...life's rule, not mine :)
I'm guessing your PS Audio phono stage is the GCPH phono stage which is no slouch. That phono stage sounds pretty darn good and if you try to replace it (without spending a fortune) I think you might be disappointed. I agree with others that said replace the cartridge. And I absolutely agree with Coltrane1 one change at a time.
If your preamp is the Ayre K1, it probably has a phono preamp in it...line 2, but maybe not indicated. If it doesn't, you can get Ayre to put one in...I don't know the cost, but it is a fabulous phono stage.
One of the challenges when asking for advice on Audiogon is that you often get way more good advice than you can practically (or financially) act on. ;)

There are a couple themes that run through the suggestions that have been made here I'd highlight to you -- first, your turntable and arm are fine -- don't bother replacing them. Second, an important part of upgrading your sound is getting a couple essential accessories -- a good alignment protractor (as Macdadtexas suggests) and (I would still argue) a good record cleaning machine. To which I would add, on reflection, an Onzow Zerodust to clean the stylus on your cartridge.

There seems to be a consensus that your GCPH phono preamp is a good fit for the rest of your system (I had suggested a phono preamp upgrade, but bow to the collective wisdom of the other respondents).

Then, look for a good cartridge upgrade oppotrunity. I agree with those who suggest a used cartridge from Audiogon is a definite option, but second Coltrane1's word of caution -- purchase only from a seller with pretty hefty positive feedback -- a lot of used cartridges have been abused. The biggest challenge you face is that phono cartridges, like speakers, have real personalities and make performance/price trade-offs. So you may want to set your purchase price range to allow you to pick two or three, and purchase them one at a time, as Coltrane1 and Lak suggest.

Hope you have fun with your upgrading.
I agree with all of the feedback you have received.I've owned many Rega tables (& still use Rega tonearms).I always found the Rega cartridge to be the weak link in an all Rega turntable set-up).I found The well reviewed and very affordable Ortofon OM-30 Super to be a significant improvement over the top-of-the -line Rega Exact.Other cartridges that have worked well for me with stock and modified RB-250 & 300 arms are the Dynavector 20x,Clearaudio Virtuoso Wood,and Ortofon 2M Blue & Bronze.All of these cartridges cost under $1000 (The Blue and Bronze are less than $500).

On the other hand,a new table can be fun.The Marantz TT-15S1 comes with an $800 Clearaudio cartridge and retails for less than $1500.I've seen them used for as low as $750.I got a great deal on a new Acoustic Signature Manfred with an RB-250 arm.
Vintage tables can be fun as well.I've been collecting Dual CS 5000 tables(I have 4)and just acquired a Thorens TD 125.The 125 fitted with a Rega or other fine arm is supposed to be a World Class Table!

Sorry about the rambling.
Thank you all for your responses. I think that I will try another cartridge.
It is nice to see the Rega P5 so well regarded. One of my issues was speed stability, particularly at the end of a side of an lp. I bought their outboard power supply which was supposed to be an upgrade in speed regulation, and I detect no audible difference. I was wondering if another manufacturer was better in this department, such as VPI.
The reason that I don't listen to more vinyl is the "software" issue. Nothing is more satisfying than a pristine lp, but I'm tired of buying at stores, ebay, etc and getting the usual 40 year old warped discs. I have cleaning fluids, brushes, etc, and the Rega record clamp, but I still find those issues limiting.