if you fancy something a bit fun you can hire Caterhams from Glasgow, not that cheap on a budget but brilliant!
Either way definitely worth having a car! If you want some good trips from Glasgow can recommend a few.
Consider some of the island distilleries for brilliant whisky and scenery!
The Whisky Regions | VisitScotland Food and Drink
Highland Caterham Hire, Caterham 7 sports car hire in the Highlands and Islands of Northern Scotland, great roads, spectacular scenery and so much FUN
Car hire and van hire in London and throughout the UK.*- Sixt Car Hire UK good prices for car rental from Glasgow airport
Edinburgh great again depends what you are into but this is worth a visit-
http://www.realmarykingsclose.com/ImageGallery.aspx
hidden underground old streets and houses!
Prague is amazing for the food but the winner and must visit is the Staropramen brewery!