I have that model wagon, but a 2010 with a manual. One of a few non-Volvo I got in close to 20+ years. Just as a background, I currently have these Volvos - 2016 XC70 & 2005 V50 6MT, and had and sold these - 2016 V60, 2005 XC70, 1996 855T, 1991(?) 944. Also had a Toyota 2007 Sienna and currently have VW Golf Alltrack 6MT. I sought the BMW E61 out because it really checked all 3 major boxes - AWD, wagon, & 6MT. I'm a wagon guy and wanted to fun wagon with a stick. 2010 was the last year that was available, so yes, I ended up buying a unicorn. I could've gone smaller to a 3 series and looked for 2012 model, but I wanted room.
What people said above is true. Check out bimmerfest.com E60/E61 forum, and there is a sticky post with an attached doc titled something like, "So you bought an E60". I read it before I bought it knowing what I might have to deal with. Luckily I found a 1-owner, very low mileage E61 where everything was serviced at the dealer. First year was zero problems. Starting second year, I had some electrical issues, but I'm convinced they were tied to leaky sunroof where the water trickled down into where they store the electrical modules under the spare tire. I had that fixed by the dealer, they moved all the electrical modules to a higher location, and all electrical problems are gone but at a cost ($$). Wastegate rattle issue will show up sooner or later - some dealers will fix just the wastegates ($$) instead of replacing the turbos ($$$$$$$). I had an independent shop do it for less ($) which is holding up ok.
I did carbon cleaning ($) and oil filter housing gasket replacement ($) as a precaution. Thrust bearing and other small issues, plus regular oil change every $5k miles @ $100 each (I couldn't do it myself due to arm injury). After about a half year of repairs and preventive maintenances, I thought about getting rid of it, but now (knock on wood) I'm looking at a stretch of worry-free months up ahead. When there are no issues, boy, this car is fun to drive. Sits low enough, handles like no other car I've had, especially with a stick shift, I'm still tempted to keep it and deal with issues as they come up. Btw, you really have to watch the speed on the highway with a stick - I get to speed limit in the 4th gear without pushing hard at all.
Compared to the Toyota I had, Volvos cost more to up keep. My 2005 XC70 was the most reliable, but no fun to drive. 944 had electrical and A/C issues, reminded me of K-car, 855T was ok to drive, had some issues, V60 was very reliable (didn't keep long) ho-hum to drive, V50 is fun to drive (6MT), but starting to cost more in repairs as the car gets older. When I get over $1k repair estimate from Volvo shop, I feel like I'll a heartattack. When a BMW dealer quotes me $1k, I let out a sigh of relief because it's not higher. I have multiple local indi shops that I comparison shop for that reason.
BMW E61 is by far the most fun car to drive compared to any of the others I've had. It also seems to have issue more frequently. It just is a high maintenance car - others pale in comparison.
In short, the reason you shouldn't - it'll cost you to up keep & fix, even if it's in a perfect condition now. Perfect conditions don't last as long as other reliable cars.
The reason you should - boy, the car is fun to drive. Comfortable yet sporty. Maybe you should convince your friend to buy it and rent from him/her on weekends. You may lose a friend so choose carefully (ha).
I never liked the bangle butt look on the E60 (sedan), wasn't too fond of E61 design, front (eye brow) or back (plain), but the look does grow on you.