Depending on where you live (or travel) you probably don’t need to upgrade very often. Do they make a lot of new roads in your area? Most areas are not changed very much from year to year. I’m in real estate and there is quite a lot of development going on here. I just updated for the first time since I got the 330 in July of 04. Depending on what I experience with this upgrade, I may not upgrade again for three years. Upgrading every year is a big waste of money and depending on where you live and how long you keep your cars, you may not ever have to upgrade.
BTW, upgrading is too easy to pay Lexus to do it for you. Buy the DVD from lexus-parts.com and take the 5 minutes to do it yourself.