I don't think that's entirely true
I for one don't have a computer that can handle MGE,
I think a lot of people play morrowind on old computers or non-gaming computers that can only take vanilla with a certain amount of adjustment.
I mean, if you look at the MGE screen shot thread, it's generally the same 10 or so people (though I do tend to stay away from that thread, it just makes me depressed
)
Running MGE doesn't mean you need to use distant land, reflections, shaders, or anything. I've never had luck with getting MWSE to run by itself, so I always use MGE simply because it contains MWSE. While having distant land and pretty reflections is a bonus, my computer isn't capable of drawing much further than the default view distance.
Anyways...
Um, I think it may be possible to check via MWSE the value of the player's inventory every time he sleeps (or better yet, changes cells, so we can have the script stop running while in menus)... You could just take the average of that or the highest value, whichever you like. Let me dig up my list of MWSE functions... If I still have it.
http://mwse.wikispaces.com/functions?responseToken=8697f3e8bdd6ac7bf91215e7b3289814
Functions you'd need for that'd be xGetInventory, xGetValue, xNextStack.
There you go.
The only reason I suggested having the thing work off of what you have equipped is because doing it by level is kind of a lame cop-out (In my opinion). And my characters tend to be poor by level 25 because they spend all their money on training rather than going out and adventuring.
Other things: The thieves guild should sell counterfeit tax papers or do something. Maybe you can even hire them to steal back your stuff? I think that the counterfeit papers should be much the same as how they deal with bounties, except you have to take the papers to a tax collector and he'd clear your owed taxes or something. Of course, there should be a small chance of discovery. Possibly skill dependent?
I further think that a C&E Office wouldn't be too hard to do, since you could just plug a door in the walls of the fort and make a simple one-room deal. Sure, it's lazy, but it seems more real when each city has their own tax office. Then again, I struggle with modmaking because I'm absolutely terrible at cellcrafting... If scripting and dialogue were all I'd need in a mod, I'd be in heaven, so I understand if you don't want to do this.