A-P-R-S, spelled out.
Smart Beaconing and I would use that all the time. Most APRS controllers implement it and have variables you can set to adjust it based on speed, delta in heading, length of time at location, etc. On a typical road trip you'll end up beaconing about every 2 minutes at Interstate speed but it will slow it down in traffic or when you're parked.
But most digipeaters and I-Gates will ignore packets if you send them too often anyway. If you set your beacon to transmit any less than 2 minutes you might get 50% through typically. Although most will be repeated locally, so your location to other hams will update, just not all of them get to the Internet.
My experience is that 5W is sufficient most of the time but you'll want to use an external antenna. I generally use 10W or 15W for the APRS side if I have it available. It seems to increase my received packet rate by about 25% through lightly populated spaces. There is no reason to use >25W ever, if a digital signal isn't going to make it with that then 50W isn't going to be enough.
"Why does the U.S. care which flag will be hoisted on a small piece of land thousands of miles away?" -- Ron Paul