Can I piggyback on this thread to ask a question about upgrading a low-end mountain bike? I have a 2005 base model Rockhopper that I bought because I wasn't sure I would like mountain biking. Today I am sure that I will eventually love mountain biking, but the reality is that I am never going to have a ton of time to spend doing it, because we have to drive to trails, and we are both busy and overscheduled as it is. So it is always going to be a once-in-a-while hobby, and I don't think it is worth it to me to buy a better bike.
But I would like to do some upgrades, mostly because the bike weighs a ton. It is the same frame as the Rockhopper Comp from that year, but I don't remember if that bike was also heavy. All the components are very low-end, though, including easily replaceable things like the stem, the handlebars, the seatpost. (All no-name.) I hate the Tektro brake levers and I've wanted to upgrade them ever since I bought the bike. I am not sure I need a better fork, and that seems like an expensive upgrade anyway. I don't hate the shifting although there is a definitely a knack to getting out of the granny gear; the front derailleur and/or front shifter lever is a little fussy. That gets easier the more I practice so I can live with it.
This may be too broad a question, but basically, what things are worth upgrading and what things aren't? At some point it might make more sense to just unload this and buy a slightly better bike, but I would rather avoid the hassle, all things being equal.