I have said it before but I maintain the GTi/D is good value if you are fairly sparing with the options... when you start stacking lots on it adds up - fine if that doesnt bother you but I am comfortable with mine costing £26.5k all in with Roof, PP and Winter pack less discount.
When I chose my options I thought what would I use a lot - heated seats in winter, roof in the summer and the PP to make sure I have the best possible mechanical spec. Everything else is nice to have, but I hardly ever need a sat nav and all the other things like reverse camera, keyless go, lane assist are all just things to go wrong at some point IMO. If you are a music fanatic and drive lots then go for Dynaudio, if not dont bother !
Changing your spec will for sure delay your order by several weeks, my dealer confirmed to me yesterday if I now added Nav, it would push back my build by "weeks"