That amp is one of the Sansui classics, if not the best known. Keep it, and, if it needs a service, get it done.
Your LP12 is also a classic. Depending on the arm and cartridge, it is still worth serious money. Selling and going for a Rega or Technics would be a serious downgrade. If you're not really interested in high end HiFi then sell and keep your existing gear. If you are interested in quality sound, then keep the Sansui and the LP12 and sell your old gear.
The LP12 is a reliable turntable and, once set up - not as hard as dealers want you to think - doesn't need touching for years. The experience of the user above is the exception, not the rule.
Don't know about the speakers. Had some for a while bought secondhand off a uni in NSW so they might have been clapped out, but to me they didn't sound super special. A friend bought them and still uses them, so they can't be that bad. Big sound - some comments here:
http://www.pinkfishmedia.net/forum/showthread.php?t=66808. Anyway, if you want to put money somewhere, assuming the amp is fine, then put it into the speakers if you don't like the Celestions, but think a couple of levels up.
Up to you, but I'm seriously jealous, mate!