If you're not going the Mountune route, then the Dreamscience intake offers a decent performance and audible improvement - you'll need a decent intake if you're planning on chasing anything beyond stage 1. The DSCi intake uses the same style of intake as they used when tuning this lump for the RS and it sounds absolutely savage
Trouble is, all the decent CAIS are around £400, Intercooler is around £500, Downpipe and sports cat is £500, then your catback at £445, by the time you've bought a remap (Let's say the DSCi - £625 for their Stratagem unit) you've spent nearly £2.5k and still only have a car that is around equal in real world performance to a Mountune'd car - only you've spent twice as much.
This is where you realise the value of the Mountune system. Of course, future upgrades are a worry, but take it from an ST owner - My Stage 1 Bluefined ST was fast enough and was on the limits of what is exploitable by the the standard chassis IMO - and the Mountune kit produces a faster car (although, IMO a more usable power delivery).