Ok gentlemen - here's my honest review of the Fechheimer MLB Pro-Style poly-spandex pants compared to the Smitty.
*Disclaimer* I've only owned one set (meaning plate and base) of the Smitty poly-spandex. So my observations are limited to the two pairs I have owned. Maybe I bought some from a different batch than you and that's why I experienced the things I have.
Construction: They have a more heavy-duty feel without actually being heavier. The pants just seem higher quality to me than the Smitty's.
Fit: @Chris Hickman is right - the cut is a lot better. I only wear base pants on the bases (not combos) and the legs on the Smitty base pants were too wide. On windy nights, the flapping of the pant legs drove me crazy.
Appearance & Color: Chris said they're slightly lighter but I can't see any difference at all. Maybe I don't have the right light but they seem the same shade of charcoal grey. Also, and this might not be true for everyone, but they don't have a shiny look about them like the Smitty's do. Mine always looked like they were starched even though I always washed them at home and hung them to dry. And there is no permanent crease.
Price: They are more expensive than the Smitty's but I feel it's worth it. They are $79.99 now on gerrydavis.com instead of $89.99. I know that's still $20 more than Smitty but you'd just have to decide if the differences are worth the extra money.
For me, I think they are an upgrade to Smitty. I'm happy with mine and will be wearing them this season. So bring on the comments!