I think a pretty pointless title is Legendary Survivor. Sure it's cool to display but it's just a grind to get to so much experience without dying. And with lag spikes coming out of nowhere, you could be 1k experience off and lose all that work. To me it's just not worth it.
Another pointless title? Legendary Defender of Ascalon. Cool statue, neat to display, but pointless just the same. Yay, you death leveled to level 20 in Pre Searing and went to Post so you could put the statue in the Hall of Monuments. I had a character that was trying to get that title but it didn't get past level 9 due to the Charr. Too much work/grind for me, but if you enjoy it, go nuts.
GWEN titles? Ugh, nothing but grind. The most they do is increase the effectiveness of their PVE skills. So while not completely pointless, they can be boring due to the grind. Same goes for Luxon and Kurzick skills as well as Sunspear and Lightbringer.
All titles are grind fests in some way, but there are some that are expensive as well. Examples? Legendary Skill Hunter. However, though it's expensive, I find it to be a good title; you get access to every elite skill in the game because capping it unlocks it. This is good for using tomes and heroes. So while the title is expensive, I think it's beneficial in the long run.
Sweet Tooth, Drunkard, Party Animal, and Wisdom titles are also expensive, but they're not as beneficial. The most you get from those is a cool statue, but I still hope to get Sweet Tooth and Wisdom someday, and perhaps Party Animal. I'm selling all my alcohol because I don't drink in real life so I won't drink in the game either - might as well sell it or trade it for the titles I want.
Protector and Guardian titles aren't bad, unless you have to repeat the missions numerous times because you fail. One good thing about Prophecies missions is that you can do the mission and bonus separate. Too bad the others aren't like that.
Cartographer? Yay you uncovered every pixel of a continent and probably used Texmod to do it. But hey, at least your map isn't all blurry.
Speaking of that title, the Kind of a Big Deal title track is okay, but it's a lot of grinding adding up to one big grind. Personally I focus on individual titles rather than what will get me to the next tier of the KOABD track. And it works.
I know there are more titles, but this is all that I can think of at the moment. So feel free to share your thoughts!