In my experience, there is only one product that really works: Techron. You will need to go through at least one tankful of gas. If you are going to go on a long drive, that's the best time to use it. You don't really want to add it and just let your car sit, or you may have to go through a second application (once the first tankful is consumed).
Just keep in mind that Techron does a great job in cleaning the system, but it isn't going to make any Spider faster than when it was new, and these cars are not fast off the line. Once they get going, they are great...
I agree that Techron is a good product. "Seafoam" also has a good reputation. However, if the fuel injectors are really clogged, the ultimate is to remove them and have them cleaned ultrasonically and flushed with solvent.
I sent the injectors from our '84 Spider to Cruzin Performance. The turn around time is quite quick - a week or less. There are other places that offer the same service - google fuel injector cleaning.
Another item that might be affecting your car's performance is the VVT. Your's should have the solenoid activated VVT. The solenoid has an in-line fuse (I think...) and the solenoid itself has to be adjusted for proper operation. Info about the VVT is in the Spider L-jet page (see my signature block for a link).