I loved L5R. It's the first tabletop RPG I played and one I GM'd for a while over on (another roleplaying site). Mainly though I've played in it. That and the card game, but the RPG was better. I ran my game under 3rd ed revised. The 4th ed book was beautiful, but I only ever tried a single game or two under that version of the system.
Personally I think there are probably enough books out there for it already. It's fine as it is, though the card game was hard to keep up to date with because they kept bringing out more and the old cards would fall out of use for tournaments and things. I only ever played in one card game tournament for it and some people sure know their decks well. They play it crazy-fast. I actually had to read my cards. It probably drove them equally crazy.
Anyway, personally I think the game has reached its pinnacle. If I was to run it again I'd look at 3rd ed revised or 4th ed, and not invest in more books. Just my 2c.