The current Vex part selection is very limited. I think we need smaller parts of various shapes to be able to build Hex Crawler and walker robot models.
I agree on the need for more diverse parts. I’m also wondering if anyone has come up with some way/shape or form to make a differential or worm gear? If so please post. 
I believe that i heard that IFI is coming out with new part for vex sometme soon, and I heard that that kit should contain a worm gear, and a rack and pinion gear(s).
there is something called steel tec its kind of like an erector set that has a lot of angles and and smaller bars that have the exact same hole alingment has vex but the holes are round it works good to make claws and the like.
Some more information about it is available here: http://www.chiefdelphi.com/media/photos/25361
Also, a little known fact is that LEGO gears will mesh almost perfectly with Vex gears… 
Antique Gilbert and Meccano Erector Sets also have metal gears and a myriad of parts that can be adapted to work with Vex. The round holes match the Vex squares and the gears are easily adapted by bolting the Erector Set gears with holes to the Vex plastic gears. Now you have the choice of square shafts vs. round shafts. These Erector Sets may be found at your local antique stores, on E-Bay or even rusting in a friend’s basement.
WOW, art that is crazy!
im sure you can make six legged crawlers out of VEX… but worm gears, i have to agree, would be really nice. if VEX comes out with a worm gear/ rack and pinon gear kit, im getting it no matter how much i have to pay
ive built a six legger:https://vexforum.com/t/walker-with-stinger/12349/1
Wow! That Hex Crawler Bot is coool!!!
Here is a large Vex Gear attached to a JUMBO RC Servo, which used to rotate or pan my Hero 2007 Robot’s head (Sensor Platform).