I took a look yesterday @ SPX weekly options b/a spreads and they still look wide compared to SPY options.
Keep in mind both the size difference and the fact that you can usually trade just off mid if it's a true mid with a mm on both sides.
I may give them a try one of these days, but I like market orders and I don't think that's going to work well with the SPX options. But watching them today, the spreads on SPY's were 1-3 cents and the SPX's were 40-80 cents.