Chris
I agree with what carlo has said above about 10k training (I've never raced a 5k!), I would also look to throw in some hill reps, decent fartlek running and some strength work in the gym, both core work and upper / lower body weights. I've got a weights circuit which I try and do once a week when training for shorter distances. Because it generally follows a lower body rep with an upper body rep then there is no resting time between sets of reps which is quite good aerobically as well.
I think it's essential to get below those times you've mentioned for 5k / 10k to have a good chance of a sub 3h30m but it's perfectly doable over the course of the summer, good luck.
As for me, very quiet week this week. Gentle 20mins spin on thebike and cross trainer on Weds and nothing since. I cancelled yesterday's swim due to a serious hangover and had a gentle walk instead! My knee is still quite sore on the outside but I'm going to be swimming & cycling over the weekend and if the legs feel better then will take in a 40min run mid next week. I've got UK Ironman 70.3 tri in 6 weeks so will be taking in a couple of shorter tris before then and will look to Abingdon marathon in October for a sub 3h20m (gulp) which is the qualifying time for Boston next year.