This is probably the dumbest question ever...
 

have been looking around to replace the sound system in my WR1 much like several other posters here. However on looking at various head units I noticed the Alpine CDA-9833R which although expensive at £330 seems to have 4x 60w output. If I were to put reasonable speakers in the front and rear (similar to my 605CS that I had in the old STi) would I need an Amp with this head unit?

Need is a subjective word :D

In short, you wouldn't need it, and you'd gain the most by changing just the speakers and the head unit. If you did add an amp in the future, you'd get an improvement but it wouldn't be the same leap as you'll get by changing your speakers and h/u

Cheers,
nick.