Have you tried splitting the ABD - EDB section into two i.e. ABD -DEE & DEE - EDB? or even ABD - DEE & DEE - DON esp if returning on a through train from Dundee to Doncaster.
Personally I'd recommend the flexible off - peak fare as this keeps your options open. You could then make more stops on the return journey as required (obviously depending on time & lighting conditions). I came down from Aberdeen yesterday morning (09:07 dep) to Edinburgh and the scenery was spectacular (due to the perfect lighting conditions). My travelling companion stated "...why does anyone travel abroad when we have this on our doorstep?.....". This was especially true at
Lunan Bay, the section from
Carnoustie to
Wormit, & the
Fife Coastal Section. As you are travelling in the morning sit with your back to the engine (window seat obviously) for the best views as you head northbound.
Not to knock Aberdeen but personally I think there is more to do/see in Dundee. I fully expect some champions of the
Granite City to leap to its defence - this will be good for the OP as he'll get different views and more local information. Aberdeen is a busy working city, the Scottish Oil & Fish capital, there's always something going on in the busy harbour. There is lots of Georgian & Victorian architecture to look at if that's your thing - esp down the wee side streets off Union Street. Old Aberdeen & St. Machars Cathedral are also worth a look. The station has recently been done up quite nicely too.
Dundee is a bit smaller and easier to get about. Don't be put out by the area immediately outside the station, however. Dundee has lots of interesting buildings in the town centre and is the home of Jute, Jam, & Journalism. You shouldn't miss Discovery Point the home of
RRS Discovery the Dundee built converted whaler that Scott used for his ill-fated trip to the Antarctic. Dundee was the last town on the Island of Great Britain to be taken by frontal assault (1651 during the Wars of the Three Kingdoms) and this is commemorated in the
Steeple church to be found by the Overgate Centre. Nice pub at the top of Union Street - the Trade Winds or Four Trades - can't mind as I'm sometimes four sheets to the wind when I venture in
. Broughty Ferry is worth a side trip if you have the time now that the service has been increased.
Plusbus tickets are available for both cities.
Don't forget some of the smaller stations en route. Montrose with its large tidal basin for birdwatching, Arbroath with the ancient Abbey - also home of the famous smokey (yum!!), & Carnoustie a pleasant coastal town if you're into Golf.
Lots to do and see so my tip is stay flexible.
Have a great trip,
Cheers