Yes, the 3.6 upgrade is much more cost effective than building up an earlier motor IMO.

Don't get me wrong, building up an earlier motor is more fun than plopping in a 3.6, just not as cost effective.
-Chris

That is a decision that only you can make for your self.

If you want a reliable, civilized, torquey motor w/ knock sensors, high compression etc. go 3.6,

If you want to modify, consider what it is that you want when you are done. A modified big motor will always beat a simlarly modified small motor, given that the weight difference between the lightest 2.4 and heaviest 3.6 isn't all that great.

Keep in mind that the further from stock you go, other systems will often need to be modified

If you enjoy the process only and are happy w/ what the motor was like when new , do a rebuild.

I went with a non-vram for my conversion & I'm very happy with it + thats in a fat pig carerra.

As others have noted its easy to upset a lot of more modern cars with this conversion and thats with the 3.6 in stock form, if you find a good engine at a reasonable price then you have an even better platform to move forwards with.

Heres a vid of mine on the dyno to help you make your mind up:
http://video.google.co.uk/videoplay?docid=-5459873911545893667&q=porsche+dyno+test