I was waiting for someone to get an ecomodder link for a grille block.
I've been running a grill block on my '99 Audi A4 for years. Went for nearly a full block to start with, watched engine temp with the ScanGauge, had to open it up a bit more to keep it reasonable around town. Did some A-B-A testing for mileage and appear to have gained 1-2mpg at freeway speeds.
Besides, I think the car looks better for it. (I think that Fiat grille pictured above looks better too)
Don't think it really changed how fast the engine warms up. Thermostat doesn't open until up to temp, so the cold fluid in the radiator doesn't matter.
If anything, do it for looks and/or mileage gains. But I wouldn't do it without a ScanGauge to watch digital engine temps, not just a sweep gauge that may barely move from 180F to 210F.