The springs do 'go off', that's for sure. I changed mine for Hyperpro progressive springs at around 15K (I think, was such a long time ago). Immediately you change, you notice that the sag was bad.

Another thing to play with on the standard forks is the oil, it is very light, 5 I think. Hyperpro provide a 15 weight oil to use with their springs. I reckon you could improve the feel considerably by just replacing the oil (which reminds me, mine could do with a change). All the pre-load does is 'take out the slack', it doesn't change the way the bike dives at all, the stock springs are linear so it's the same compression force though out the spring compression, unlike progressive that requires more force as the spring compresses.

With progressive springs front and rear, the bike is totally different to ride. Well worth the �150~ it cost.

On my XTR I had to go to 15 weight fork oil to
get any thing that looked like damping.. got
rid of most of the springy efect.
15 weight oil also works well with 40mm long
pre-load spacers.. but ended up makeing new
valves with adjustable compression & rebound damping..
Just wish the rear was as easy & cheap to sort out..

http://img233.imageshack.us/img233/8521/ssa41922.jpg
By petenz at 2012-05-25

http://img812.imageshack.us/img812/2962/ssa41924.jpg
By petenz at 2012-05-25

http://img140.imageshack.us/img140/7093/valvef.jpg
By petenz at 2012-05-27