MDR -
Back in the golden age there really seemed to be three types of gamers. RPGers, BGers and those nuts who fought out Napoleonic battles with miniatures. While most people didn't necessarily find themselves locked into one specific group, I noticed that peopole who played SPI games rarely crossed over into
RPGs. Conversely, most nonboardgame fanatics stayed away from SPI with the exception of some of the "easier" games like The Creature that Ate Sheboygan or some of those capsule games.
My gaming group was fell into that category as well. We played only a few SPI wargames back in the day. Ironically, we were huge Star Fleet Battles fans - played every Sunday for about three years straight (and none of us like Star Trek). And that game is the model for overly thick and complex rules systems.
All that said, SPI had a huge and devoted following. It seems they still do today. Just check out SPI games on ebay and you will quickly see what I mean. Basic run in the mill SPI products consistently go for big bucks - especially compared to the likes of Victory Game, AH and others.