Re: Town Portal abuse - it's time to end it.
I don't know if this has been adressed, but for the ability for party members to join the party quickly, though without the ability to abuse tp's, how about one-way tp's. You cast the tp, people from town can go down to you, but not the other way (back to town). That'd also be very logical as then demons and stuff couldn't follow you back up.
For ways of returning I'd suggest a different skill, very costly teleport mechanism, as it should really likewise be one-way only, but also for a single person only, because otherwise creatures would be able to follow (the way it's in diablo 2 makes no sense, some guys cast a blue portal, monster storms after guys, guys go into blue portal, monster stops and wonders where guys are).
In boss fights and other places where you should not be able to leave quickly, there could be an anti-teleport field, which means you would not be able to teleport back to town, you'd still be able to create a tp to get reinforcements, that way if you fall in battle you'll also be able to quickly come back, but you can't return to town.
Then there's the "problem" with combining the new tp type with the teleportation back to town, however as already mentioned where the new tp's would be very cheap, the teleportation back to town would be expensive, other types of teleportations, such as you can teleport items you find into a very large inventory of yours would solve the problem of filled inventory space, however again these means should be limited, so some kind of tactics would be required.
So making the trip back to town too expensive to abuse, and impossible to use in major fights, but still make it possible for other party members to join and items to be transfered to your stash, would kind of solve a lot of problems if you ask me.
Maybe you could even make a range, which means if a tp has been cast in an area you can't teleport back to town unless you're in a radius of x yards away, now for non teleport areas against major opponents, one could imagine that the major opponent would actually create a tp of its own from where demons/undeads/animals/etc. would be summoned, whereby completely preventing the ability to teleport out. Likewise as objects are now an important part of the game, one could imagine the major opponent would start off by destroying some wall so you can't get far enough away to leave battle.
So what do you think of a system like that? How expensive should it be to teleport back to town? It should probably be based on character level if you ask me, and make it harder as further you've come into the game on the same time, maybe make zones, in stead of basing it on character level, however if you don't base it on character level, people would probably start rushing big time again.
You could also set a level-limit (or in stead of level-limit then maybe a limit on the quests you've completed or something like that, something that actually measures your own skills) on tp's so other people can join you, that'd also be a major hindering in rushing.