Traveller has always been one of my favorite science fiction RPGs. One of the hallmarks of Traveller is its dedicated fanbase and the fact they have supported the game continuously since its publication. First with Fanzines, then with mailing list, finally through a succession of websites. There may have times when there was nobody publishing Traveller material but there never been a time when the fans were not doing something with Traveller or its quintessential setting the Third Imperium.
The most cost effective method of owning older Traveller material are the Far Future CD-ROMS
Of all the subsequent editions The Mongoose Traveller Core Book is the most worthy successor to Classic Traveller. However their supplement quality has been spotty (but improved in later printing). At all cost avoid the 1st edition/printing of Mongoose Mercernary.
GURPS Traveller has the best supplements, like their historical books they are useful even if you don't use the rules. GURPS Traveller:Nobles, GURPS Traveller:Far Trader, and GURPS Traveller: Solomani Rim are particularly good. The only real dud in their line is their version of the Spinward Marches.
The Traveller Map is an incredible resource. Probably the best one ever made for any RPG. It even allows you to pick any of the its sectors and download it in a booklet form that is similar to the original Classic Spinward Marches. Some of the utilities can be used with custom data that you created for your own Traveller setting.
To me the Old School Renaissance is not about playing a particular set of rules in a particular way, the dungeon crawl. It is about going back to the roots of our hobby and seeing what we could do differently. What avenues were not explored because of the commercial and personal interests of the game designers of the time.
What are RPGs?
A game where the players play individual characters interacting with a setting with their actions adjudicated by a human referee.
Rules are an aide to help the referee adjudicate actions and to help the players interact with the setting.
Dice are used to inject uncertainty which make a tabletop RPG campaign more interesting than "Let's Pretend".
The only thing a player needs to do to roleplay a character is to act if he or she was really there in the setting in that situation.