I've read and read on both the 535i and the 550i debate for E60s.

But would love to get some quick thoughts on where the better value is? Or none?

2010 535i (with just the heated seats, everything else is base, no shadowline, no parking sensors) - 6 speed manual for $5,900 with 173,700 miles.
vs.
2006 550i (with parking sensors, heated seats, sport-seats, but not m package) - 6 speed manual for $7,000 with 130,360 miles.

Both body conditions are similar, has some minor scratches, knicks, bumps and bruises for the age.

 

The determining factor for me would be how well they were maintained. Do both sellers have receipts and maintenance records? Are the Carfaxes clean? How many owners have each had? If you have never owned a bimmer before, they're not cheap to maintain, especially the 550. Make sure you know what you are getting into.

 

N54 is going to cost you a fortune to run. It is a money pit. Good for tune if you need a weekend ride. Make sure 550i was properly maintained and go for it if you don't care about pre-facelift interior and awful CCC (if it has one). I never saw n54 with such a high mileage. That must be a survivor (perhaps never been tuned).

 

Utter rubbish. I've had my 535xi since 2012 and put 80,000km on it - 230k now. I replaced the water pump and thermostat once, front tension arms and brakes - these are maintenance items. As for actual failures, I had a bad crank position sensor and a radiator with a split in one fin. It has original turbos, old index 5 injectors, and the HPFP has 200k on it - and I run it with JB4.

 

I am really happy that you car runs like a champ. You have one vehicle and I have dealt with over (60) of them. When people ask me to code used injectors or non latest revision I politely decline. One indirect way to tell engine reliability is to look as the number of revisions for given BMW part. You just don't see end of life parts for no reason. The tooling cost is really high when the new revision comes in. For instance fuel injectors had 12 revisions! This is the only one that is worth replacing with. In fact BMW came out with the latest revision of fuel injectors after they stopped manufacturing these motors! They had so many problems that BMW didn't even know how to fix. Thanks to N54 on the large scale why BMWs have a such bad reputation. I do love N54 as they made more money on them than all other BMW engines combined (this is not my source of income btw). Would I recommend someone to buy 277k km N54? Never!
N63S (early ones) is another great example of unreliable engine. Since they are not nearly as popular you don't hear about them as much.
For references I have seen many N62, N62TU running perfect past 170k miles (not without proper maintenance). I have yet to see N54 with more than 110k not running rough or with some other issues. These cars depreciated to a point where they became a new honda civic. The fact that one can gain 100hp with minimum investment gives teenagers serious erection, but doesn't help with reliability.
PS: if I was you, I would order replacement water pump today (not tomorrow)!

 

For every 'bad one' you read about on the internet, there are hundreds that are fine - very few people complain when things are working. I'll drive mine daily until something breaks, then decide if it's worth fixing. Bad reports like yours keep the value down, so I'll be able to find a 'parts car' for next to nothing.

The extra 100hp is better than a blue pill at my age...