Experience gear can cut your play time by a lot, but you must keep upgrading your gear or else the bonus experience will not be enough for your current level. Having multiple sets of experience gear every few levels will help. However, you do not actually need full sets, just a few pieces to make a difference on your next character. Additionally, if you are running out of space and do not want to upgrade your shared stash, you can keep them by creating a few extra characters and passing the gear to them using the shared stash. This will also save you money, but it is recommended you eventually upgrade your shared stash to avoid wasting time moving items between characters.