Welcome to FTE! I'm doing a similar resto on my truck and going for a stock look. If you want to have a mostly original look with subtle upgrades for driveability, you can get that with the original engine and tranny, and like other have said, it will be cheaper and less hassle. That stock 6 can give you decent gas mileage (15-20mpg) and reasonable power. You won't win any races, but it doesn't sound like that's your objective.
Here's what I've done (or am planning to do) with my truck to improve safety/reliability/driveability while holding onto the stock engine and tranny:

1) Upgraded brake master cylinder from single to a dual reservoir unit
2) Replace front drum brakes with disc brakes (an F-100 can be done with a $400-$800 kit from any of the truck catalogs)
3) Rebuild the stock rear drum brakes
4) Rebuild stock steering ($450-$600, components readily available)
5) Radial tires
6) Change rear end ratio to a more highway friendly gearing
7) Pertronix ignition
8) Rewire everything with fresh harnesses and a modern fuse block (kits start at under $200 for this).
9) Replace the generator with an alternator (For your 1955, upgrade to 12V from 6V).
10) Add seat belts and headrests

If the stock engine and tranny are in decent running condition, you can improve reliability by refreshing all the surrounding components. The deeper you go, the more reliability you'll get. Think about taking the radiator to a shop to be rodded out or recored. Change the hoses, belts, and the thermostat. Replace the water pump, fuel pump, and oil pump with new units. Have the stock carb rebuilt. All that can be done without tearing the engine apart and rebuilding.

Value is another story. If you're trying to make money in this hobby, you're fooling yourself. Almost anything you do will ultimately work out losing money. The best way to lose money would be to take a good solid original truck, chop it up, then modify it poorly or loose interest and leave it in pieces.

If you do end up going modified, my opinon is that the farther you take a truck away from stock, the number of people who will like everything you did gets smaller, especially if you're an amateur builder like most of us and your work is less than Chip Foose quality. If you happen to be a Chip Foose kind of guy and build perfectly crafted hot rods, then your professionally built modified F-100 will certainly be worth more than a well restored original F-100.

Good luck and keep us posted!