I used ETF back when I did my room, I don't think RoomEQ Wizard was available then, but it's the same idea. It was quite helpful and enlightening. You can also get some generic info from simple room mode calculators. I posted all the measurements and so on that I did on my web site. It's been quite a while and it was a lot of work, but I think it was worthwhile.
As far as "does room treatment make a difference?" I'd say it depends, you might just accidentally be blessed with a great sounding room, in which case, you're all set. Most of us are not, so it can make a big difference. Here's the difference room treatment made for me, in my garage - a mono recording with 1 mic 18 inches away:
Empty garage:
http://www.dougyoungguitar.com/mp3/1..._bare_room.mp3
And then exact same position, when I was about 3/4 done with treating my room:
http://www.dougyoungguitar.com/mp3/F...3_18inches.mp3
The foam vs 703 or other materials is just a matter of math. You can look at the absorption coefficients, and if you have measured your room, you'll know what you need. Foam absorbs mostly highs. if that's what your room needs, it will work great. Most rooms need broadband treatment, or even mostly lower frequencies tamed, and foam would not address that. I have a tiny bit of foam in my room - it's strictly for cosmetics - it looks cool, which is what it does best :-) The real work is done by the equivalent of about 30 OC-703 panels and corner bass traps.
Someone mentioned in another thread about the difference between recording and mixing, and that plays a role, too. I do my You Tube videos in an untreated room. With close micing, a basic carpeted spare bedroom works "ok". I wouldn't record a CD there, but it's good enough for you tube. But I mix those videos in my treated room where I can hopefully hear better.