Hey Jeff, welcome to the depot
.
Well there's a bunch of things you could do depending on your budget. As you've done the battery mod I'm assuming you are ok with some soldering
.
The noise mod is worth a look. Basically replacing a bunch of electrolytic capacitors which unfortunately degrade with age so this one is a bit of a no brainer.
Depending on the use the units had, the input jack would have taken the most wear and tare, so worth replacing. Is it a "top switch" Ver 1 unit ? (where you can change the output from inst level to line level ?) if so then the rear jack mod is worth doing.
The MDRT replacement transformer (available from MJMP here (http://www.marshalljmpmodshop.net/miscellaneous_parts_and_replacement_tubes.htm)) really opens up the unit and helps with noise.
You can change some (or all) the opp amps for better specked versions. There's a post on here somewhere where a member changed all the opp amps and carefully researched each one for the best he could find, he reported it sounded better than new...
My friend MikeB bought a new (stock) tube board from MJMP, so gold plated tube sockets and better/modern components. Actually Mike has done all the above (except the opp amps) to his Ver 1 MP-1 and it's sounding great
.
To reduce the gain, IIRC there are some trim pots for the OD stages
you could tweak. Or use lower gain tubes (either just one (and V1 would be the go) or both). Or even use a 12AU7 or 12AT7 in V1 instead of a 12AX7, others have done this.
Apart from that, if you don't already, run it in stereo (makes heaps of difference) with a decent multi Fx unit.
Hope that helps..