MOTM

For me, the joy of synths comes from these sources:

1. coming up with an idea for a useful module, could be based on some  
existing piece of hardware
2. figuring out how to actually build the thing, usually with a  
breadboard
3. making a board layout
4. building a prototype
5. testing and tweaking the prototype
6. building the final version
7. using the new module to create sounds

With a fully assembled module, I only get #7. With a kit, I still get  
to build it and test it. And there's always the possibility of hacking  
in some modification or tweaking some resistor values to enhance  
functionality (like the Oakley OMS-410 or Larry's 110 VCA resistor  
tweaking). That's not so easy to do with an assembled SMT unit,  
especially if you don't even get a schematic with it. So a kit, even  
if it's just a board and panel, is still a lot more fun than a "plug  
and play" unit.

However, I'm not completely opposed to assembled units. I have the  
Encore Electronics UEG and FS, but in those cases they weren't  
available as kits, and there wasn't a good DIY alternative at the  
time. I'm not biased against the 520 and 730 as assembled units, but I  
would look for DIY alternatives if I considered those to be "must  
have" modules.