Hi elainem. My experience exactly. I really did feel that the Blackrock guy was trying to sell me the maximum no matter what; whereas his Crumlin colleague was trying to help me do the mimimum. When the latter came back to look at the damp plaster, his comment was that the "cure was worse than the disease" - whereas B'rock guy - who's coming round next week to take another look, wants to rip the entire wall apart. I don't know who the hell to believe!
All I know is that the surveyor from McGovern's, who kindly gave me 15m of his time on the phone, was very reluctant to attribute the problem to rising damp. While there is general consensus that it does exist, most experts would say that it is quite rare.
I would hazard a guess that your floor puddles are condensation caused by your leaving something on the floor - water vapours getting trapped between the two surfaces. It sounds - no matter what the cause - that you definitely have higher than normal humidity in the room - so do put in a dehumidifier. We got one with a visible humidistat, so you can see what the average humidity in the room is. It's been on for a week, and we've gone from an average humidity of 70, down to 50. Be warned that your plants will need more watering, though! This should hopefully bring things under control. We found that Argos had a good range of models - DeLonghi and eBac have good reputations.
As to whether to tackle the damp before selling - I would ask myself whether the buyer will be likely to be doing major works to the kitchen. If you think they will, then why go to too much expense in the kitchen when your works will probably end up being dug up anyhow? If, however, you think that the kitchen is a selling point, then by all means solve the damp problem first.
But for the sake of your peace of mind - I would define a reasonable point beyond which you will walk away from the damp problem - otherwise you could be trying to solve it till doomsday! Hopefully the dehumidifier will stabilise things in the interim.