This is just my personal opinion - the value of which may be only as much as what i was paid to offer it:
If I am buying a snowmobile I would much prefer doing the fix up work myself rather than having a former owner slap on a band aid only to find out later that there are bigger issues under the surface. (Like the one sled that came in looking pretty good but ended up that it actually had a bent crankshaft that shook the engine apart)
And, considering that every sled we bring in at a minimum receives new pistons, rings, jets, fuel needles, fuel line, filters, gaskets, and carb flanges - this alone equates to about $300 in parts and a day's worth of time. So on that basis, and reading between the lines above, it probably makes the most sense for you to offer them for sale as is.
However, be forewarned, that if you do decide to start down the road of fixing one of these sleds - even if you are only saying to yourself that i am fixing it just to increase its value so that i can sell it - you run the very real risk of contracting the dread condition colloquially known as Mad Kaw Disease. Be equally forewarned, there is no known cure or antidote -and a plethora of crank seals are, at best, only symptom relievers.