I've done several day trips to Edinburgh, by rail from Suffolk and I've always found it worthwhile. (I've used an 'All Lines Rover' ticket which I used to get very cheaply when I worked for a rail company). There's plenty to do and see. Full information is here:
http://www.edinburgh.org/
However, from my point of view, the best thing about Edinburgh is the Wetherspoon's pub ('The Standing Order'), on George Street, which serves great real ales and superb haggis, neeps & tatties ;-)
If you're flying to Edinburgh airport, you'll need to know how to get to the city centre:
http://www.edinburghairport.com/portal/site/de fault/menuitem.1509e57cfbd378f73bcdea10c02865a 0/
I've not been to Glasgow but I know many people who've had a great time there:
http://www.seeglasgow.com/
To get from Glasgow airport to the city centre, see here:
http://www.glasgowairport.com/portal/site/defa ult/menuitem.07debed571aba8f73bcdea10c02865a0/
Ryanair fly to Prestwick, rather than to Glasgow. I've considered taking a day trip myself, but I've decided that the airport is too far away from Glagow. The official Prestwick website is down but travel details can be found here:
http://www.prestwick-airport-guide.co.uk/trans port.html
Chris