If you want to provide a comfortable living for the guy who sells fuel, buy a fixed gear aircraft.
Also, we're talking experimentals in this thread, aren't we? So you're not gonna be buying an old airplane and paying a mechanic to fix it, we're gonna be buying a new-ish airplane and fixing it ourselves.
Several problems with this argument:
1) You're burning a couple of extra gallons per hour to go the same speed - if the Arrow had the same speed mods your Pathfinder does, it'd go about the same speed or better - The Arrows I've flown with the tapered wing and straight tail, ie the III models that are basically equivalent to the Dakota, flew at least as fast as the Dakota or beat it by 5 knots on 35 less hp and a couple less gph.
2) Not only are you burning extra gas, you've got two extra cylinders to maintain. Not a huge deal at annual, but when it comes time for engine overhaul, all else being equal, you'll more than spend the difference that you may have saved on all your annuals. (I say "all else being equal" because IIRC you have a carbureted engine. The Arrows are fuel injected. That makes a big difference in overhaul cost too - But that's a PA28-specific thing.)
3) Speed-wise, otherwise equivalent airplanes (Lance vs. Cherokee Six, Arrow I vs. Cherokee 180, Mooney G vs. D, etc) tend to gain 10-20 knots when given retracts. So if we forget the apples-vs-oranges-that-look-like-apples argument you've presented here - You're wrong about the nil speed difference.
4) Weight-wise, while retracts do weigh more, I would bet that in this case the weight of the retract system on the Arrow is lower than the two extra cylinders and the extra gallons of fuel you'd need to carry for the same trip.