I'm three seasons into my first V-P, which is a 1998. Zero repairs, just self maintained with fluids, lube and filters. Shop that handled the PP inspection didn't raise any concerns about Volvo being a challenge on parts and service. They work on them as a staple of their existence. Please expand thoughts on how Volvo would be less desirable than Mercruiser? Having owned and operated many Mercs, I'm more comfortable with them. But I love my DuoProp so far.
The one you have is a good bit simpler than later models. Some of the issues with Volvo are parts prices (really excessive for certain things) and availability. Also, to me putting the trim pump in the transom shield OUTSIDE the boat in the water was a major mistake, vs the previous design, this started with the model that followed the SX (SX-A). The Ocean Series Drive (Composite) was a disaster that they walked away from, with problems with failed bellows and cracking transom mounts etc.
They do things I really dislike and force you to buy new complete components when they could be rebuilt and can be rebuilt with Merc's and even old OMC Cobras.
Example, steering actuators (commonly leak on the older models), they say hand over $1,000 for a new one, meanwhile some enterprising folks have figured out how to replace certain seals to repair it
Trim cylinders, same thing, I was able to rebuild 2 OMC Cobra trim cylinders for the cost of 2 $55 rebuild kits and about 3 hrs of my time.
Oh and that trim pump in the transom mount? It's over 2 grand.
Watch out for NLA parts for their EFI and electronic ignition parts. I have seen people have to go out and buy a cast iron 4bbl intake, an Edelbrock or Holley carb and go from an un-repairable EFI system due to no parts, back to a simpler carb. They used a Prestolite BDI system for while that you can't get modules for either.
I think service where I am is widely available for both, but I would check what year the drives are on the boat that has VPs that you might be interested in and then see how easy it is to get parts you might need.
As a general thing, depending on the age of these boats, I would not want any of them, if they have cat converter exhaust, this has added a new modern car style headache in terms of check engine lights (O2 sensors are not meant for wet exhaust) and if you have to replace the manifolds or the catalyst, the prices will stun you. Someone I know had to replace one on a 4.3 Mercruiser and the parts price was about $4500. I have seen prices for both sides of a Volvo 4.3 exceeding $6000. If I bought any more I/O boats they would have to be old enough that I could avoid that nonsense.
