How important is the mic preamp? (And/or AD converter) in the home/project studio?

Hey all, I wanted to get you your opinion on mic preamps - now with all of these integrated audio interfaces coming with their own mic pres? (I just purchase a steinberg UR28m http://www.steinberg.net/en/products...ies/ur28m.html and obviously all these manufacturers pride themselves on their excellent preamps. I want to make commercial grade recordings, but do I really need to shell out thousands on mic preamps and ad converters when there are so many decent audio interfaces out there that can get the job done - after all, with a good performance, tone, and production I've seen stunning examples of great recordings done on lower budget gear.

I just wanted to get some thoughts on this ...

Thanks

Slinkyfran