We will visit Edinburgh, Glasgow and Stirling Scotland in late Feb and would like to see another location. Friends have suggested: Inverness, Perth and several others. Any suggestions.
February is a tough time of year to be traveling about Scotland, if you're relying on public transportation. With a car, it's a lot easier. If you fancy going farther afield, Skye has become a 12 month place to visit, and Mull could be a possibility. There's more of a chance of the Mull ferries being cancelled for weather than for Skye, especially as you can drive to Skye.
You may want to check out the Falkirk area for the Kelpies, the Falkirk Wheel, the Forth and Clyde Canal, and Callendar House. Heading up the east coast wouldn't be too bad an idea as well. You could visit St. Andrews, Crail, Anstruther, Dundee, Stonehaven, and Aberdeen. Dunnottar Castle, just south of Stonehaven, is spectacular in any kind of weather. There are also several castles in the Aberdeen area, some of which should be observing winter hours.
I was in Scotland in late February each year from 2001 to 2006, and never encountered any really bad weather. It was cold, but just dress appropriately. I hired a car each time, and never had any trouble getting about. I did hit one snowstorm in Aberdeen in 2006, but just drove slowly and sanely.
The best thing to do is to keep an eye on the weather forecast. If heavy snow is forecast, best to stay to the central belt. Otherwise, you should be able to get about with no problem.
Best wishes and stay warm!
Personally in February I'd rather rely on public transportation because driving on ice, on unfamiliar roads, would make me extremely nervous. Scotland may not get a lot of snow at the lower elevations, but below-freezing temperatures and frequent precipitation make icy roads a strong risk.
How much time do you have for your additional location? Dundee is not far from Edinburgh, and from there you could take buses to Glamis Castle in one direction and St Andrews in another.