We sold our 2005 3.0i X5 last year and I am so glad we did. I too carefully considered what E70 variant to replace the E53 with. We drove a 2011 50i but it had some long island rust and I was afraid of the maintenance requirements.

The diesel seemed attractive and I was very tempted to buy a board member's here... but again the very complex and expensive emissions parts scared me away. Diesel is currently over $7 in my area vs. $3.50 (with stop and shop discount!) for 93 gasoline.

Ultimately we bought a 2010 30i m-sport from California (totally rust free) and paid to ship it here to Connecticut. Has adaptive drive, totally worth it. Wouldn't buy one without that option. MPG is 16.9 which isn't great obviously. For us, it's the best model choice even though it feels underpowered.