My two cents here. You said it youself, your summer/performance tires are quite pricey, so why not start the season off with a balance (check to see if you dropped a weight last season??) and an alignment, make sure that you use a shop that knows how to align the X5 (apparently there are issues!! might even be a good idea to use a local dealership, if you need any parts or work done, you can decide to either do that yourself, or have an indy shop do it , or if the price is right, the dealership.)
I always bag and tag my tires each season, I also wash and wax the rims inside and out too, makes them look new when i put them on next season!
i store my wheels inflated to proper pressure, and on their sides stacked in the shop out of any direct sun in their bags (thank you kal tire!!)
after a rough winter its a good idea to give the suspension a thorough once over so your summer season is as pleasant and surprise free as it can be!

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2003 X5 3.0i (02/2003) sport package, Sapphire black metallic / Black Dakota Sport seats. compass mirror retrofit, trailer hitch retrofit, Prodigy P2 trailer brake controller installed, PDC retrofit, Lumbar support retrofit. heated rear seats retrofitted. Running boards retrofitted and subwoofer install in progress. 4.8is Brakes installed front and back. Bluetooth TCU installed, Rear Fog lights installed. Retrofitted reclining rear seat backs.