First of all, here is my favorite synth... a Roland SH-101
Not much to it, monophonic, no midi, a wild animal. Love those analog beasts. I've had many including a beautiful Arp 2600 which was completely uncontrollable, but so much fun!
Often I will re-amp a modern synth to give it the gritty character of the old analog beauties, but only if there is room in the mix to do so. Synths can have a tendency to take up a lot of space because so many patches are stereo. I'll try to go mono with placement to keep them from being space-hogs. Because of the imagination put into many synth sounds, I love to really juice them up by panning them wildly across the picture, or drenching them in reverb and placing them in the far background.
Re-amping is useful because it can make a relatively boring patch sound like a human is really behind it. I use small guitar combos for re-amping in the booth at my studio. Favorite re-amping amps are my little Piggy and Valco, seen here... more awesome gear toys on my "Gear Porn" page: Sylvia Massy Gear Porn