Hmmm I wrote a long reply to this yesterday but it seems to have disappeared or never appeared.
For your return journey, if time is not much of a consideration but money is, have a look at http://www.irishferries.com/ie/sailrail.asp or http://seat61.com/Ireland.htm for details of the sail-rail option.
If you follow the booking links on either of those websites (or, I imagine, on nationalrail.co.uk) you will be able to find the ferry and rail options, which costs €51 or GBP 38 provided you buy it at least a day in advance. Note that the Irish Ferries site charges no additional booking fees but it does not itself provide details of the rail connections.
This would involve sailing from Dublin at 14.30, arriving in Glasgow at 23.18, with changes at Holyhead, Chester and Crewe, so it would be a pretty arduous way of saving money.
However, the nationalrail.co.uk site does not provide this option, I'm not sure why - it only gives you one that will get you into Glasgow at 9.14 am the next day. That may be because it doesn't trust the 14-minute connection time in Chester, or because there's something wrong with one of the connections raileasy.co.uk is promising.
Even more arduous would be the later option, leaving Dublin at 20.55 and arriving in Glasgow at 10.36 am the next morning. This option costs €45 or GBP43 (no idea why one is cheaper on the UK site and the other on the Irish site, though I think the Irish one is more likely to be correct).
Unless the plane is ridiculously expensive, I would go for it - if it's a business trip, surely your employer will pick up the tab anyway?
Also bear in mind that the ferry terminal at Dublin Port is surprisingly far away from the city centre and you need to allow for check-in time - so you would have to leave the city centre by 13.30 to be on the safe side.
Bottom line is it's possible but you'd want to be desperate.
Edited by: fear_rua