I mix strains fairly often, but I stagger them and I always start with the strain that I want a certain ester profile out of, then after 30-40% attenuation, I pitch a raging starter (made with wort from the original beer), and let the fermentation finish up. I do this with Saisons, Weizenbocks, and some Belgian Strong ales. So in the OP's case, I would have pitched the 1388 and let those nice pear/tropical notes set, then followed up with the 3787 for a quicker attenuation.
I hardly ever reuse the yeast that results from these beers, except for Saisons, and even then, subsequent beers never have quite the same winey character that the first batch will have when I use this technique (I usually mix 3724 and some other Belgian strain for a quicker fermentation without fermenting at 95f).