For what it's worth the DA convertor chip in my RME UFX is also used in a Presonus interface that costs quite a lot less.
What you principally get with higher end interfaces is not just better convertors but better electronics supporting them. There isn't however a whole series of steadily better and better convertor chips as the price rises, certainly not when you get to RME, Apogee etc. The other thing more money tends to buy you is lower noise analogue components and circuits and better preamps.
I ran a comparison a while ago between my UFX and an old Cakewalk badged UA-101. The UFX pres and line inputs are good for at least a 3dB reduction in noise per channel and if the specofications are to be believed a bit less distortion each. Which hardly matters if you rarely work with more than a few recorded tracks and do most things ITB. It does make quite a difference in the summed noise floor and headroom if you are working with a dozen or more recorded tracks. In your case that may not be a factor.
If you need a couple of mic inputs, a couple of line inputs or so and a flexible mixer for it (including built in reverb, delay, dynamics and eq all of which can be printed or sent to the monitor bus only) I'd suggest considering the RME Babyface. RME drivers have a well-earned reputation for rock-solid performance at low latency and while no-one knows what the future may hold, RME have a history of supporting their products for a long time, rather than discontinue driver support when an operating system upgrade occurs and point out your old interface is now a brick, so you'll be overjoyed to hear they've a new interface you can buy.
Once you get to RME or UA etc. you're already into the region where the returns per extra dollar get smaller and smaller. An effect which increases more and more as the prices go up.