My other 1/2 has an '00 Rift Zone, which I bought for her & has had depressingly little use. It has 24 gears, Manitou forks & v-brakes. We are off to Wales in a month & I am wondering if it is worth improving for her (if it feels safer/ more controllable she may go on more trips). As she is fairly cautious new brakes spring to mind…..that means new wheels. That might be good for me as it also potentially gives me the use of a different wheelset….which in turn could mean a 9 speed rear mech/shifter. Then there is the problem of hose vs cable guides.

Are all disc rotors of the same size usable with all brands of calipers (I have XT centrelock discs & XT calipers)?
Can 8 speed shifters/derailleurs run on 9 speed casettes?
Is it all a waste of time/ money & I should just get a 2nd set of wheels?

PS what tyres for N. Wales in August!

I loved my '00 Mount vision, but it came with all the upgrades your talking about, I definitle say there worth it… at worst they could always be transfered to a newer frame.

The best upgrade that I did though was to replace the manitou forks, though I put MX comps on which did make it slightly slacker (longer crown to axle), getting a set of Reba set at 80mm would transform it and maybe having the rear shock upgraded with a push service to stop pedal induced bob (assuming it is a fox).

p.s. one of these frames came up cheap in classified a while ago, I was too skint to buy it, but would have if i'd had the cash.

Are all disc rotors of the same size usable with all brands of calipers

Basically yes. I'd recommend Deore discs as a good budget option.

Can 8 speed shifters/derailleurs run on 9 speed casettes?

No

If you want to upgrade her bike then do it, if you want a second set of wheels get them, but I wouldn't say it's worth it trying to combine the two, unless you make her bike 9 speed, otherwise it'll be a reet faff. Also, unless you get the same hubs you already have or shim your rotors you'll likely have problems with discs lining up.

You might get the deraliuer to go to 9 speed, but the shifters wont do it, see if you can get a 34t 8 speed cassette if you think a slighty lower ratio will help, V brakes work pretty well in the dry and if she isnt flying…. seen what looks like decent wheels on the bay for about £70 with Shimano hubs and wienmann rims if you did do the disc upgrade, and they come in colours so can match the bike and look more bling than their sting…

zippy has a point about maybe longer forks would slow the steering up a bit so might make it feel safer, especially at speed.

you can run an 8spd cassette on 9spd hubs as the spacing is the same so your sorted there. As for rotors and discs why not just get some cheaper shimano brakes that use the same size rotors as on your bike and you should be fine. It may be best to use the same hubs as your main wheelset too because different hubs can be spaced differently and you dont want to be setting up your brakes every time you swap wheels do you.

Edit: to clear things up you keep the 8spd cassette that is on the marin and only run that cassette on the marin.