Fergie,
I would never want to disagree with DnD or GnO, their combined posts have been some of the best advice I have ever read anywhere. However, how you use HAM is the largest variable, as you know.
For myself, I purchased a VX6-R Yaesu, and could not be happier. For trail use, the wattage ouput is adequate, and the antenna is a magmount. I also have a tri-band antenna for true handheld use. For motoring, if all the wires bother you, run battery only, and have just the antenna wire attached. Battery should last all day, if you're not a motormouth.
What I really like about an HT is the multiple use factor. I hike with it. Loan it out to other trucks, have it by my bedside and listen to nets, take it with me on trips, etc.
Although wattage is important, it is not all that important. There are a lot of variables, but, for instance, the difference between 50 and 75 watts is not that large. Strength of signal is not a linear function of wattage.
I have not heard this discussed, but as I see it, communication happens when two parties can hear and be heard. If one party has an exceptional receiver, and a great transmitter, then he can clearly communicate with a person with a weaker signal and a poorer receiver. That would be me, in some cases.
For instance, I enjoy going to the Channel Islands, and take my HT with me. There is nothing quite like sitting in my tent and hitting a land based repeater 60 miles away, and talking to someone from, well, most anywhere. This does not speak to the strength of my HT as much as is does to the quality of the rig the repeater owner has installed and set up. And, of course, I am at sea level, and the repeater is several thousand feet up. (some are upwards of 7,000 ft.)
Now, what is obvious by my choice is that I passed on the $100 option and went for the $250 option. But I went for an HT. And, spent another bill or so getting all the other stuff. Works for me.
Concerning dual band, I really like the added ability to reach out to more repeaters. In Southern California, there are a lot of repeaters on several bands, notably 440. In an emergency, it certainly gives you more options.
Also, dual receive can be helpful. I know of some who use this feature on the trail. In one case, a couple can ride in different rigs, and still have their "private chat line" when one carries the HT, and the other drives the family wagon with the dual-bander.
After all that, I would agree with many, and say that a mobile is a likely first choice, unless you have reasons for an HT.
Dale