I've spent a few days questing hard to purchase -0.5 rings. After doing so, I tidied up my quest information, and worked out roughly how much drachma was left in the game for me and how much I'd spent.
Basically what I found out was that I've spent 3000 drachma, and there is still about 2000 left outside of quests run by the immortals. I have already purchased all the optimum ac gear apart from a -1.4 helm and -0.4 + MAX_DEX guards which probably won't be better than -1.3 and -0.8 alternatives. So basically any further investment in drachma eq is already not in my class specific function now.
Given the main advantage of rebirth is the ability to redo quests, it appears that all this drachma will achieve is add mana regen or the odd MAX_STAT to mostly already optimum eq. Secondary improvements... Given the changes to scrolls, and the running less of epics, and the further rank gains having little power gain for effort, already I am questioning... is there any rush to rebirth? I don't think so...
Rebirth involves a further investment of 450b xp and 890m gold (the gold cost is probably worst), before you get back to where you were. Unless you wish to use the double xp bonus to buy things quicker from the avatar shop, you'd really need to be spending more than 225b of xp to make rebirth "worth it."
I'm not sure that rebirth is worth it, unless a player wishes to "replay" the game essentially for the fun of it... so I don't think anyone should be in any hurry to do so, and only do so with a lot of thought. I think there are 5 or 6 rebirths now, and 3 or 4 thinking about it, so make your decision wisely.
I'd be Interested to hear some feedback from 9x40's and rebirthers now we already have a 6x40 rebirther.