As long as you're staying on property, you have to figure out the best way to use emh for you. Unless you're a super morning person, getting up an hour earlier is more taxing, especially as busy as you are on a Disney vacation. That said, if you pick and choose the emh days that make the most sense for you, I think the advantages are worth it, and I think crowd increases are fairly negligible.
Magic Kingdom emh we have found particularly useful. Because the left side of the park opens at 9, you essentially get two rope drops which help you get a lot more done quickly. And with evening hours, there's a lot of attractions with wait times that aren't too bad. The other parks could have emh advantages for you (we're going to try epcot morning hours next month, and are forced to do Animal Kingdom morning hours) but those don't stand out so much to me. It just depends on your plan and situation. But as long as you can be there on time (or stay there late), I wouldn't let fear of extra crowds discourage you.