This is a great question. It opens up all kinds of topics for debate.

It seems you already recognize that it doesn't feel normal to be under boost at cruise. This is a good instinct to have. It can be a sign of a mechanical problem with the engine, transmission, even brakes...or it can be normal.

I live in Colorado, and most of my cruising is done at elevations of 7000+ feet above sea level. Up here, the air is so thin, boost is required to maintain anything over 75MPH. Depending on where you live, if the air density is greater, you may not notice this as much.

It's likely not a problem on your car though, and likely not going to cause damage either. Volvo engines, at least in factory condition on the 700s, are Light-Pressure Turbos (LPTs) so even if your boost gauge is half way between the center and the maximum it ever reaches, you're only under a couple of pounds of boost. Just watch your gauges, especially temp and oil pressure! Propellor-driven aircraft will often employ a LPT configuration similar to this to allow them to operate more efficiently and at higher altitudes. Other turbocharged engines, however (like my roommate's 1999 Mitsubishi Eclipse GS-T) operate at much higher pressure (~16 PSI) and should not normally be much above 0 PSI at cruise.