I don't think it'd be worth it for maintenance alone. Maybe if you wanted to turbo it, etc, but the maintenance can't be that different, honestly.
You'll have 2 less spark plugs, and a little less oil for your oil changes? Timing chain v belt, sure, but the TB on the 3.4 can usually last WELL past it's 90k intervals, won't hurt anything if it DOES break, and isn't all that hard to do yourself. My dad and I did mine in about 8 hours, and that included a lunch break, pausing to watch portions of MBTIM's video, creating the crank/cam bolt breaking tool, and 3 separate trips to the store, plus trying to dodge rain drops. I'd say my next TB chnage could be done in half the time.
The 2.7 has a distributor, which itself needs to be maintained, and typically distributor ignitions are harder on wires and spark plugs due to the higher voltage. So you'll theoretically need to replace those more often = more maintenance.
MPG gains are negligible. My stock 188k 3.4 v6 can still just reach 23 hwy if I baby it. I average around 19-20, and I'm none too light on the pedal.
You have to swap the motor, the tranny, the mounts, probably the exhaust (at least pre-cat), probably the belt driven accessories, wiring harnesses, etc.
That plus any timing tuning involved due to the distributor, and any possible CELs to chase down, due to the swap itself, etc.
That's a whole lot more involved, both in cost and labor, than just doing basic maintenance on a pre-existing engine (or even a swap to another 3.4, which will pretty much just be plug and play).
