I would wait for the 73s to be in and running before booking a trip on them. Note how the 92s were quietly canned.
Feb might provide some beautiful snowly landscapes, but equally the poor weather might lead to delays and cancellations on the remote routes and you don't want to spend a day on a replacement bus!
Also worth noting that it has been reported that weekend FW sleepers in Feb are going to run to Oban and not FW. So whether the 'day' leg will still be available is not yet clear. The other services do not offer internal fares so are not available with this ticket, although apparently you do get a 10% discount on a sleeper fare, so you could use on the first or last day.
http://www.railrover.org/pages/freedom-of-scotland-travelpass.html
As for value for money, you need to do some careful planning to get the most out of the ticket. It works out at £34 a day for a 4/8 ticket. Inverness to Thurso for instance is pretty much a full day expedition. Leave at 7.00, back in at 5pm and with an advance ticket it would only cost £24, so on its own woud be a waste, but run it as one of your spare days or go back to Aberdeen or Edinburgh and it becomes more attractive. Given the sparse service in many areas, you will need to plan all of your trips in advance anyway or risk becoming stuck.
How much you enjoy it depends what you enjoy doing. If you want to see loads of different trains then it is not for you - nothing but 15xs on most routes and almost all in the same colour schemes. But if you enjoy beautiful scenery and collecting difficult trackage then there is a lot to enjoy up there.
