Definitely go! I honestly think they'll be easier at this age than at 3yo (they'll have many of their own ideas and opinions at 3yo - right now you're pretty much still calling the shots). Just do everything for their age, take it slow, lots of shade, naps, water - you'll have a wonderful time!
For our first trip, mine were dd(3 1/2yo) and ds(21 months old) - and tons of other people on this board go w/ toddlers, babies, infants, big kids, etc. It was a heavenly trip, but we took it sssllllooooowwwww and not once did either have a meltdown or tantrum (but honestly, even if they did, so what). We would have simply dealt with it. we did early mornings in the parks, always had lunch ressies for 11am or 11:30, whenever the restaurant first opened up (but counter service would have been fine too, but I really suggest the 11am or 11:30am lunch - no crowds), then left the parks usually for naps and pool time. sometimes we'd go back into a park for an afternoon parade or the evening, but not stress about rides. maybe a fast pass or 2, shows, walking around, etc... or we just hung at our resort watching bunnies and ducks on the grass and chasing lizards. The kids were in heaven!
It's honestly harder w/ a larger span in the ages of the kids than with twins - having an older kid have to wait for the younger one to do dumbo, or having to wait with the little one while the older kid & one parent does splash mountain, splitting up parents to please different ages, etc (we'll go to toon town, you go to tomorrowland and we'll meet up). At least w/ twins or kids w/in a couple of years of each other, you're all on the same page. Mine are 21 months apart, so not too bad and we always were able to be on the same page (except for the boy/girl thing, which has come into play in recent years - they're now 8 and 6). DS is no longer happy to see Beauty and the Beast, and dd is not interested in star wars and car crashing shows (me neither!), but there's enough for all of us to enjoy together too, and of course we compromise.
You don't say if you have boy/boy, girl/girl or one of each. If you have the same sex, then you really have the best of everything for a disney trip! And even if not, it will be perfect (and it doesn't matter for years anyway w/ the boy girl thing)! Go and enjoy!! You'll be amazed at how much they love there, and you'll not regret going (just be sure to plan ahead and take it slow).