You should caaaause thieves are the best class
That's new as of April 15th, btw. That patch had a whole bunch of QoL changes.
I see this misconception so often that I really think it would be worth tweaking the LFG tool to depict the total number of ongoing LFG runs visually somehow.
When a party fills up in the LFG tool, that listing is immediately removed from the finder. This happens so quickly and frequently that it appears as though there are only 2 or 3 groups up per dungeon at a time. Try posting the listing yourself- unless it's one of the more obscure paths in the game, you can literally expect a full group in a minute or two. Making your own also lets you control the comment, which can make a big difference in the kind of PUGs you get.
Leatherworking isn't such a profiftable craft for selling so far as I know, but since you're over 400 already you're almost to the point where you can make the once-a-day Ascended materials. These are:
- Lump of Mithrillium
- Glob of Elder Spirit Residue
- Spool of Thick Elonian Cord
- Spool of Silk Weaving Thread
Because players can only craft one of each once per day, these will always have value on the TP and can be sold for profit regularly unless you're saving for Ascended gear (not recommended yet if you're concerned with money).
Outside of that, good sources of regular income are dungeons, the world boss/daily rares, PvP, and merely gathering and selling valuable mats (
http://gw2spidy.com is a great site for seeing what stuff is selling for).
A daily bout of quick dungeons is easy to get into and the guild does them frequently. If you learn CoF1, CoF2 and SE1, that's nearly 4 gold in barely over a half hour. Add in SE3 and AC paths, and you can be swimming in profit for the evening. Note that the big gold and token bonus for dungeons is a daily reward, so repeating the same path is not really profitable. You can also buy rares (or exotics from the lower level dungeons) and salvage them for Ectoplasm for even more silvers.