I've decided that my next tour will involve my old MTB, which is currently setup as more of a hybrid commuter. Nothing on the drivetrain but the chain has been touched since it was new 20 years ago, though, and is in sore need of replacing.

It currently wears an Acera-X rear, the older metal style derailleur, not the newer plastic-y looking ones. Not sure what the front is, it simply says SHIMANO and a seattube angle range. 7spd 13-28 rear cassette, 3spd 44-34-28 crank.

My specific questions:
1) If I am changing things out, is upgrading to an 8/9spd setup worth the extra effort?
2) Do I derive any benefits from new derailleurs, both if I upgrade to more gears (Acera seemingly should go to 8 without issue) or if I don't? Neither is broken, both work fine.
3) For climbing, is there a consensus on whether it is better to have a big back gear, little front gear, or both? Hills aren't my forte, this will be a new experience. Also, again, does that answer change if I go from 7 to 8/9?
4) For any parts I do swap out, what is the level at which parts are of decent quality? I don't mind paying to get out of junk range, but I don't buy into something automatically being better because it costs more.
5) Any recommendations on cranks that have arms that look more old school, plain metal bars, not curved space-agey looking things as seems common these days? I'd like to remain with 3 chainrings, probably keep a similar gearing.
6) What sort of shifters do people prefer with the butterfly/trekking style bars? It currently has SRAM MRX Comp grip shifts, I have no idea if I can change out the cable without destroying them. I'm not particularly in love with, nor do I despise, any style of shifters.