Lucy, You've obviously been clocking up the miles! I don't know that a visit to swanwick will give you anymore useful info except maybe a smattering of knowledge about sector groups and airways within the uk. You can get this info without the visit so i'd stay in sunny devon rather than battle my way up the M27! (food's rubbish as well) Make the most of your aerodrome visits and have a few stats about each place ready for your next interview. runway designators (i.e. bournemouth 26/08 etc), the types of a/c you saw on the day, the approach radar facilities and the co-ordination required with area control centres etc will give you ample ammunition for your return visit.
Once again, good luck.
RP45