Without knowing the years of them, the Gary Fisher has a better aluminum fame than Trek has, but Trek has better components, personally I would just stay with the Wingra and save your money, so you'll have money to do upgrades to the Wingra as needed. The Wingra came with Acera derailleurs, those derailleurs are not a long term component, so at some point you can upgrade to the Deore, or to the SLX, or maybe to XT.
The one thing to note if you decide to go the upgrade route is that the top of the line XTR shifters are fantastic, but that's the only thing I would buy from the Deore high end XTR line, if those shifters are too expensive then go with the XT shifters; then jumping down the XT the only thing I would buy from that group is the rear derailleur due to the derailleur using bearings instead of bushings; the rest I would just use the SLX stuff has being the sweet spot to be between price, long life and weight; then I would stick with the basic Deore cassette it's made of steel instead of aluminum and will last a lot longer than the more expensive upgraded cassettes will last, and also Deore chain will last longer than the others will. Make sure you use good cable housing, the Shimano sp41 cable housing can make a world of difference as to how your components will feel, in fact if your bike is having some shifting issues, try those cable housings first before buying new stuff and see what happens.
A word of warning about XT shifters, as of 2 years ago? they had a problem with a spring breaking causing complete shifting failure, I am not sure if that situation has been addressed yet, but I would hope so by now, but maybe someone here has a better answer for that.
The Shimano Deore hierarchy from low to high end is Deore, SLX, XT, and XTR, but other than the shifters there's not need to splurge on XTR, or even XT.
The other thing about bikes is that you need to get an approximation of how many miles have these bikes seen, aluminum fatigues with miles and weight which means a bike ridden 10,000 miles by a 135 pound person vs the same bike ridden 10,000 miles with a 225 pound rider, that bike with the heavier person could already have aluminum that is already tired out. Of course if the bike was ridden 50,000 miles with a 135 pound rider the frame could be tired out as well. Stupid things to consider before buying a newer bike.
If I were you, I would just keep the Fisher and slowly upgrade it as needed.