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.
adnan
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.
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.