$2000 To Upgrade System

just my op but consider room acoustics, cables and vibration/resonance control first.this way you could discover more about the gear you have before spending big bucks on one area. i bet your system sounds pretty good already. what music do you like and exactly what are you trying to achieve with this upgrade?

We don't know what kind of sound you prefer.
Naim/Devore, Plinius/Proac, Creek/Spendor ?

I think I'll go the amplifier/speaker route first. I'm a relative newbie at this, but I'm not sure how much an upgraded phono pre or cartridge would help the sound when played through my budget amp/speakers. I realize my TT is outclassing everything else in my system so I feel like I'm not hearing it's full potential. Any speaker/amp suggestions in this price range?

My first impulse would be to change the cartridge. $500-600 will buy a very nice cartridge. Then spend the rest on speakers.

I think you're fine with the turntable and speakers you've got. I'm not a big fan of Bellari phono stages, and I haven't heard the Marantz unit. If it were me, I'd start by auditioning amplifier options. The Naim Nait 5i with a Rega Fono MM would fit your budget and be worth a comparative audition to see if that's a direction you like. I think it would make a good fit with your Rega front end and the well-timed, well-balanced Wharfedales.

I wouldn't have said this a few years ago, but how about a integrated with a inboard phono ? It would have to be from a manufacturer with a history with analog. A Creek and Rega passed through my hands awhile back when I was inbetween gear. They were good performers and the phonostages were not an afterthought. A few less connections in the chain and a better power supply (in some cases) also.
Look for used (recent models) here for that and take your time shopping for speakers after. That really can be a personal thing and you would have a solid foundation to evaluate behind them.
Just another way to look at it.

I would say speakers/amplifier first, cartridge/phonostage second. And possibly cables too. Another approach would be to start with the cartridge/phonostage and then work your way downstream. In any case, it appears that your turntable is the strongest component.

Looking at your system, I would say in order of importance, upgrade the speakers first, then the phonostage/cartridge, and finally the integrated amp.