I think there are 3 differences here with what Neptune is doing versus MAAM or any other museum operation -
1) The two planes will remain as fire bombers. This means they can be their own act, doing demo water drops at any airshow, including to help put out the grass fires the Blastards start with the Wall of Fire.
The other P2V's out there are all in military config, and that's where the "never heard of it" comes from. The P2Vs as fire bombers are actually pretty well known, especially in and West of the Rockies.
2) The company can "subsidize" the operation of the 2 Neptunes with its other operations. Museums either need really gracious donors, other "money making" aircraft, or good appearance agreements to be able to operate such a complex aircraft. We all know this is hard to do even with big crowd pleasers like the B-29s, so it's no suprise it's nearly impossible with a P2V.
3) Having 2 aircraft still in operational condition with current crews means that if there is a surge requirement during the season or when they have planes down for maintenance (or during the "off season") then they have aircraft they can quickly put on short term contract and get the job done.