choices...long and wordy sorry
A couple of thoughts.
I'll agree with marcus, I would not make it a daily driver unless you just like to drive it every day, but I think it is best left as an occassional driver to really enjoy the performance envelope. Driven every day, you will become numb to the cars fun....opportunity.
I own two. A completely stock 98 speedster and a 95 coupe that had the factory R components later in life. Yes, by the time I had bought the 95, the engine had already had the weak pistons exposed.....kaboom, new engine with much stronger components. The personalities of the cars could not be more different. Stock '98 could be driven every day.....has no vices. The '95 is like an angry animal that enjoys being hammered. Does not idle all that well.....hates to have the A/C on at stop lights.....but holy cow, it goes, stops and corners like no ferrari, shelby or porsche I have ever owned. It flat out runs away and demands your TOTAL attention if you are going to take advantage of its potential because it far surpasses the performance envelope of any other car I have challenged.
Both are great fun to drive, but as the 95 already has 18K miles on it, it is my usual choice. It can be tooled around ( but not happy about it) in but I prefer to enjoy it in brief spurts.....not bringing too much attention to myself to save a nice driving record....and cheap insurance.
As far as investment potential, there is no camparison....at the moment and I don't think that will change any time soon. The s351 cars are the holy grail of sn95 saleens (some would argue that it is not earned) but neverthless, the badge sticks.
I collect older mustangs as well. What was collectable 5-10-15-20 years ago is still the same. The values have changed, but the desire of people to own "collectable" versions has never faultered.
Lastly, buy what you like to drive. Don't factor in investment prospects...because when the darn thing breaks....the investment potential goes in the garbage can.... Huge frustration just sets in.
Good luck. Look at as many as you can find or just buy a nice clean Cobra, you can't go wrong in that case. They are great cars.
Sorry to be so verbose.
Dan