I've found that speed can dampen the warmth and other unique characteristics of MDMA, and make it feel more like just a regular stimulant experience. However, (as mentioned) if you've got mongy MDMA, it can put a bit more of a spring in your step, and get you dancing. I'd suggest taking the MDMA, and then deciding if you need any extra stimulation, or saving it until you're starting to get tired and using it to keep you going. It's certainly not a shit combination, however it's done, but I'd definitely give the MDMA a chance, first.
Regarding speed and booze; I love the combo. The booze takes the edginess away from higher doses of speed, and even though it stops me getting pissed, there's still some synergy between them. It's pretty much been a daily thing for me, for a long time, on and off, and it's still an enjoyable experience, as long as I know when to stop. It's very easy to keep doing lines and drinking for a few days. As Julie said, if you hammer the booze, it'll leave you with a mighty hangover, more than likely whilst you're still wired, which is a bit of an ordeal. I've found that allowing the speed to wear off, and slowing your drinking down, until you're tired, helps prevent such a scenario.
If you're not reckless with speed, you shouldn't get much in the way of a comedown, except needing to catch up on sleep. I've found that a lot of people that say it gives them evil comedowns are the ones who've hammered loads of it at once. Everyone is different, however, so I'm not going to say that it's only those that overdo it that suffer. I get off very lightly, despite the fact I take rather a lot. I only really suffer when I run out, after taking it every day for weeks/months on end, as I end up in withdrawal, which lasts for a week or more. I do love the stuff, though!
