And so it begins...again.

I agree with Inas there, I hate the money suck that is the death of a thousand supplements. If the were constantly selling extra properties for Monopoly or new more powerful letters for Scrabble, I wouldn't play those either...

Honestly for me it depends on the suplement.

For instance take the Complete Ninja's Handbook by the late Aaron Allston, which is all kinds of awesome. It does introduce new rules (or rather adapts them from Oriental Adventures) but not as many as you'd think and mostly things that had to be introduced to the basic campaign for a Ninja class to work - martial arts and new weapons and so on.

A lot of the book however is more about actually roleplaying a Ninja (for a player) or running a Ninja campaign (for a DM) that can't be had just staring at a Wikipedia link.  He even (and this is my favourite part of the book) had suggested an alternate campaign setting using the Ninja rules to create occidental spies - basically James Bond in an AD&D setting!

That's the kind of thing worth paying IR£11.95 for, at least at the time.

Not that I can't be parsimonious when it comes to spending either. ;)

My RPG library mostly consists of the core books for any given system. I very rarely buy supplements, particularly if it is primarily focused on mechanics-based material, but I do sometimes buy campaign-setting specific stuff.

The key thing to keep in mind is most of the time the supplements are not needed, even in modern game systems, but they are offered for players interested in adding elements to their game. I have no issue with that. Variety is the spice of life, or so they say, and nobody is forced to buy new supplements.

It really comes down to having fun. If using supplemental material brings fun to the table, then by all means, knock yourself out!