According to
http://www.bbc.co.uk/news/uk-scotland-scotland-business-14186837 Inverness and the Mid Highlands had the 2nd highest growth in economic terms in the UK, 1st being the east end of London. So there is a case to increase links between Inverness and Aberdeen/Central Belt. Whether it is hourly, I don't know, certainly not half-hourly alternating to Glasgow and Edinburgh, (although a quirk of the sunday timetable means that a train from Edinburgh and a Train from Glasgow arrive into Inverness within 15 minutes of each other, both coming via Perth). My personal view would be to have a longer train with better facilities running 2-hourly fast to Edinburgh, then a slow every 4 hours to Glasgow. With an almost megabus model of all trains connecting at Perth for any other destination in Scotland.
Back to the topic of thread I think it is important that expensive re-doubling or doubling should only take place if it benefits Intercity travel. I can't see point in increasing Dore for the sake of the local trains as these can be better timetabled to miss faster trains using the line, especially when loadings are low throughout the day on local services, provision needs to be made for longer trains again at busy periods.
COV-LMS, is essential, for current traffic, for volume of freight and as a diversion route, this would be top priority in my view as there is not just a case for potential local expansion but has benefits nationwide if this is doubled.
Montrose, who knows, re-route via Forfar!! as they are saying on the Scot-Rail discussions forums. I do like the thought of having one slow train an hour calling at all stations, even if this is only a ABD-DEE shuttle, well except Golf Street and Barry Links.
Chester - Wrexham, only double if it is to be electrified, as electrification improves acceleration in turn improves frequencies with less stock.
And a local issue to me is the doubling of Beauly to Clachnaharry (Inverness Swing Bridge), as this is at capacity at the moment, and could be done at the same time as a signal renewal, as it is planned to extend colour lights to Dingwall, where RETB or future alternative would take over.