venting in upstairs toilet - help!

[thedude]

Here's my problem. I moved into a house with three bathrooms, one on each floor - basement, first floor, and second floor. I believe the second floor bath was added sometime in the 70's. After deciding to remodel the upstairs and gutting the walls, I discovered that the upstairs toilet drains into the downstairs stack (I believe its called a "wet vent"). My question is, how big of a deal is this? All three toilets have been operating without a problem since I bought the house (going on 4 years now.) Adding a seperate waste stack and vent would be a significant undertaking. Any ideas? I would appreciate any input. Thanks.

 

[Plumber2000]

Could be fine like it is, no pictures to see it, so can't say other wise, pictures would be of great help.