A compromise solution would be to use a couple of voting receivers in the locations you mentioned. Having multiple same-frequency repeaters would probably be a problem due to "simulcast" issues.
The voting receivers would improve portable coverage, i.e. they help the relatively weak inbound link, while the repeaters and base stations simply use raw power to hit the portables in the remote locations.
And yes the mobiles with decent antennas (a VHF "rubber duck" antenna actually has several dB of LOSS) would be a huge improvement over the handhelds. It would be challenging to install a modern solid state mobile in a steam loco !
73 KF5N