The upgrade from V1 Personal to V1 Commercial is $50 and like Erik said will allow you to flash in a different OS.

You could actually flash in the 2002 OS... you would copy all your tables into the new file (table-by-table, takes about 2 hours of steady work), and then you could flash this into your PCM.

V2 already includes the ability to flash OS's so you would be looking at the V1 to V2 upgrade for $499. If you do it right, you can duplicate the licenses from your V1 to your new V2 and retain the 2 unused licenses that come with V2 (i.e. your new V2 would have all your V1's licenses plus the new unused licenses).

You said that you would continually tweak... V2 is perfect for this as on the SD card ($5 from Amazon) you can store many tune files and log files.

As of a recent firmware release candidate V2 has gained the ability to full flash the LS1B/0411 PCM (i.e. perform an OS change).

Sure, the V1 to V2 upgrade is almost $500 (you would end up with 2 unused licenses and you would duplicate your V1 licenses), but you would need to spend $150 on your V1 (Commercial upgrade plus 1 license).

If you do the V1 to V2 upgrade, then your V1 will be frozen where it's at, it will not be able to accept any more new licenses (it will still retain its current licenses as a backup).