we also have the valco twin trimode w/ toddler seat and it is a life saver. my girls are almost 9 months old and I've used it since they were born, just put them in the stroller w/out the car seats. the thing is a dream, seriously. I can push and turn it with one hand even with my 3 y/o in the toddler seat. there is tons of storage space so I don't have to carry a diaper bag, I just put what I need in the baskets and pockets and go. if I need to grocery shop, or shop in general w/ the twins and my 3 y/o, I'll sling one twin, recline the empty seat and put all of the groceries in the seat.
We also have the ride along board for my 4 y/o and he really likes that when he's tired. If it is raining and my 4 y/o is in school, my 3 y/o will ride on that so she and the babies can be covered by the rain cover.
Yes, it is big, and draws a TON of attention, but I've never had a problem taking it anywhere. You sometimes have to think a little about if you are going to make it through a narrow space, but it can go anywhere a wheel chair can go, so you should be able to get through in most public places.
Like the PP said, stomaching $700+ dollars for a stroller was hard, but it is the best money we've spent for these babies, maybe even ever. it gives me freedom to do what I need to do and not have to stress to much about how we are going to do it.
PS. if you are interested in a mountain buggy urban double, albeebaby.com has some on closeout for super cheap right now... but i'd still go with the valco