In the under $2500 category, diminishing returns?

In the less than $2500 (new/used) category for integrated amps, is there a point of diminishing returns?

Here's my situation, I'd like to set up a system around a pair of Maggies (MMG) I already have. One source will be my iMac with a Music Streamer DAC. I'll likely have a modest turntable soon too (Rega RP-1). I listen to a wide variety of things, but let's just say... Radiohead
I can budget upto $2500 for an amp, but would love to spend much less than that and sink the rest into CDs and vinyl.
An NAD C 326BEE can be had for around $4-500. A Music Fidelity A5 (used) for about $1500. Would there be a 3x difference between the two? Can I get a significant upgrade in sound by spending the whole $2500? I'd like to hear your thoughts.
Room size and listening level should be considered. The A5 is around 200wpc and the NAD is around 50 I think? I've never owned the MMG's so I don't know how much power they need?
If you are planning on keeping it for several years I would say go for the better amp. Yes the A5 is a better amp. I believe it's worth the extra dollars. But hey I like spending money!
I have MMG's,thought they sounded good with 50 watt amp.remember they are 4 ohms.
But discovered 100 a side was better and 200 even better.
Now use a rebuilt,modded Hafler 500 putting a measured 524 watts a channel into 4 ohms and they sound great !

Maggies need juice,the more the better.IMHO more power is preferable to a better amp,of course one wants both-LOL .
For bellow a $1k Aragon 8008 300Wpc will drive'em near perfect. The rest of budget you can get sub and dive into nirvana.
Having owned/tried pretty much every integrated under $4K, I've learned that diminishing returns don't really start to kick in until about $3k (new list price). But you have to double the price to get 'a lot' more. A $2k is way better than $1k, $3k is way better than $2k.

That being said, there are tons of choices and system matching is very important. Don't be afraid to spend the money to get what you want, just take the time to listen and decide for yourself.

Personally, quality is always better than quantity (power) if you can't have both. Most high quality integrated amps under $3k run with 50-100 wpc, which is fine for most uses and should be fine for your Maggies. If you are looking at tons of power, expect to give up on quality at this price point.
Forgot about integrated.
Once you get introduced to W4S STI500, you'll realize that diminishing returns are almost at its best right there.
I've owned Maggies for over 20 years ,they will not do anything like their best at 50-100 watts.
The best I've heard MMG's sound,all things cosidered , is with Belles Amps,with a 150 as a minimum.
Personally I'd find the cheapest used Belle putting ot 300 watts into 4 ohms,buy that and not look back.
Balanced Audio Tube Integrated
Since your budget is $2500 a Bada Purer 3.3se has plenty of power and current for the MMG. I know it's a BAT 300k clone but it sells for around $1200(new)at Pacific Valve. This gives you $1300 for a turntable-cartridge and phono-pre. Consider a new budget Thorens table over a Rega due to better build quality.
Thanks for the advise thus far; there's a few NAD dealers around here, so hopefully I can against their stuff against some more expensive amps mentioned above locally.
I believe a used Musical Fidelity A5 (attainable for 1300.00 or so) is one of the best buys in higher-end integrateds. It would be far more dynamic and revealing of micro detail than the NAD you reference. If MF didn't change their product lines like the pope changes robes, its amps would be given the respect they deserve.
I have driven them with a Cambridge Audio 840A integrated with 200 watts at 4 ohms and now am using a Bel Canto REF 150S amp with 150 watts at 4 ohms and so far all good. I think these are probably minimum levels of performance, both are in the $1500 range. Ideally you not only want to be sure the amp selected is rated to operate at 4 ohm but also, preferably, that it will deliver 2x the power at 4 ohm loads as at 8 ohm loads.
rogue cronus tube amp mates well with mmg and is in your general range and a good value. add a sublater if needed and you have a pretty sweet rig.