cams arent really serious work.........but the benefits without proper setting up and re-mapping are quite small.
PBVs dont do much except increase baseline fuel presure with a rising rate. SO, only really give s you any benefit IF your runing lean at any point, and has the risk of running overly rich if not setup....its a crude method and better left for turbos.
Chips and re-maps can give better drivability but they only really adj ignition timings and injector fueling....so, there is limited scope and increases in power arent that high.
I would always go for heawork to increase flow (without reducing velocity) over the entire lift range. Ond cost wise, 350 quid is amuch as youll spend on all the intake exhaust mods etc and will probably give more for your buck. And it still leaves scope for more when you add more on........
But thats just me.....