WI: He had never married his niece Aggrippina? She either dies or he remains married to Messalina. Could his son by her have succeeded him and what kind of emperor would he have made?
That question is a bit impossible to answer, given that it's about a theoretical person...
On a slightly different note, could Claudius -being the glory hound and wanting to leave an imprint of his rule on the Empire- have made it his mission to permanently conquer Germania (up to the Elbe) instead of Celtic Britain?
Britain wasn't completely worthless for the Romans - there was still the population which could be enslaved. Given the fact that slaves at this time often meant an investment, so rich people would buy them even without urgent need, just as they might buy derivatives today, you see why the Romans were interested in Britain.