Will I get much more power from a new intake and exhaust?

Oh yeah. There are a couple of downsides to these mods. 1) They're illegal and 2) They'll usually make more noise both intake and exhaust. You have to be able to deal with both. I usually suggest starting off with the inexpensive Caddmann Mod to see if the additional intake noise is worth the power trade off to you. If so you can stick with that or move on to one of the aftermarket setups. Exhaust systems are always one of those 'ear of the beholder' things. Too loud to me may be music to your ears. Keep in mind every system will produce a different power curve. Some have even been known to 'reduce' power compared to stock exhaust.   

Here is a chart showing the power improvement on my Nomad running essentially stock then with the Caddmann intake then an aftermarket intake and V&H Bagger exhaust. As you'll see the difference is quite substantial.

Does a modified intake work?
This is a Dyno Chart For '01 Nomad FI with over 50,000 miles on it

Click for full size image

Run 005 (blue) is stock intake and mostly stock exhaust (bypass pipe in place of goat belly)
Run 017 (red) is Caddmann intake and mostly stock exhaust
Run 025 i(green) s Thunder Odyssey Intake and V&H Bagger exhaust