No doubt, any treatment is preferable to none.
I have just a small bedroom which was totally bare with the exception of a carpet. Do a clap test and listen to the reflections - that's all bouncing back into any live mic used.
It's now nicely treated and set out correctly and the improvement is amazing.
Also remember that sound radiates 360 degrees from your monitors - don't forget to treat the area behind them. I also have some treatment behind my PC unit to help curb fan noise.
My vocal station uses one of those semi-circular reflection filters on a mic stand, but it is strategically placed so that the mic points to the area of most wall treatment.
Finally, you don't need to spend a fortune - duvets can do wonders. Rig them up behind your vocalist or throw them over mic'ed guitar amps.
EDIT: If you decide to use acoustic tiles, have a look at this tip I posted some time back - on getting those little suckers to STICK on the wall. http://demon.acoustica.com/bbs/viewtopi ... feddcea603