If its roughly the same amount of turns lock to lock is there really a difference with a de-powered rack? A few people have run it and I haven't heard of a single failure, if one were to occur the highest load situations are actually low speed so you're significantly more likely to have a failure turning your wheels stopped than at speed. Honestly at that point though its not like the spyder is idential to an elise in the front end so its a bit random to choose unless I'm missing something, I don't know the dimensions of the racks compatibly but I know a lotus Elise is wider than a spyder by an inch so who knows what you're getting into. Realistically you might as well get a custom rack for as much as a lotus one would cost.
Here is a company that seems to do custom racks:
link
Its listed under pontiac but from what I'm reading they can do it for any application,
here I found an old group buy for S13s, if you could contact the company and get others involved (intrest has been expressed by a number of members in multiple threads on the board) you could probably get a better rate than even a used lotus rack
keep in mind I'm no expert though you've got to do your homework
-Spargo