Definitely do not change how often this guy spawns.
Rare and unique items need to *stay* rare and unique. It's really cool to finally get a title/speeder/hat/etc and anyone who knows about it will know how tough some things are to acquire and (should) respect the player who managed to do it.
SWTOR needs more things like this that take lots of time and/or effort to earn. Personally, I didn't even know about this but now it's something I can look forward to achieving and just gives me one more cool thing to do.
Frankly, now having the achievement myself I do not agree with this. There is nothing respectworthy about an achievement you can only get right after maintenance. All it states is you have either no real life or are lucky enough to not have any obligations at that time (or are lucky enough to be on a server where it is still possible to have a second Taris instance).