Isn't this how the majority of sales owners start out in life?
Buying a 90s car, making it shine, and selling (albeit.. With some shady tape repairs and meter rolling).
Its a good idea. Make sure you buy for the right price, manage repair costs reasonably, not cutting corners in vital areas (things like fibering an AC vent properly instead of buying a set is fine). Know your cars, models and their common issues and the target market.
Better if you could even profess in one specific make/model and be a pro at it. There are such people who deal parts and cars for one specific generation of the model even (for example, E36 Gen of the BMW 3 series)
Best way for you to be profitable, is to know your mechanics well and have a good rapport. The repair/paint costs will bite away at your potential profits. That's why most sales have their own workshops.
Also yes. There are always people who will pay the premium as long as they aren't sales buyyo or toyyos (the type to criticize the minor scratch under the bumper and color choice of a 40 year old car and its affect on resale so that they can post an ad on the quicksite instantly with a 25% profit margin).
It won't take so long for an enthusiast of a specific model to look around at a few beat up specimen and think "ayyo, isn't there any hope of finding a good example?" (being there, done that).
When I was looking out for cars and motorbikes of that vintage, I always come across douchebags who cant send proper pictures, don't answer calls, don't know jack about the car, can't send a video of its condition, talk with bulto in their mouth, legit boomers.
This sucks when you like the vehicle and have no choice but to make a several 100km journey to inspect it.. Only to find out it has no battery, or that it's a completely difference vehicle from the picture, or that the engine is so undercompressed it can't move the vehicle.
Your target market should be enthusiasts and you should make efforts for an effortless transaction to happen. After all, no sales, no profits.