If $350 matters that much to you, maybe it's worth it. I personally don't like Dive Rite, and lump it in with Halcyon as a once small and responsive elite-level gear company that is now too bloated to provide either the best gear or the best service; but others swear by their products and service. From what I can tell, they're better than the junk Hollis is pushing, though. I've heard a lot of good stuff about the HW Frog as a less expensive alternative to the SW Petrel.
Part of the $350 savings, however, means fewer features--at least one of which you said you want. You'll have to upgrade the Q (I think this costs money but I couldn't find pricing beyond "contact Dive Rite") to include such features as (1) PC interface cable (Petrel has integrated bluetooth that is fantastic); (2) bungiee adaptor (integrated and included with Petrel);
(3) customizable gradient factors (stock on Petrel); (4) 3 normoxic or 7 hypoxic gas OC trimix (Petrel allows for 5 preprogramed OC and 5 preprogramed CC mixes of any O2/He levels out of the box, and also allows the changing/adding of new mixes on the fly during a dive)...so no multi-gas deco diving with the Q, as it only allows two mixes.
The Q's plan mode seems to be NDL only...so you'll need to shell out the $80 for V-Planner if you want to cut tables. Though you should do that anyway...but being able to run deco profiles on the Petrel is a nice feature. The Q lacks some other helpful info the Petrel can display, like tissues, GF%, and @+5. Read the Q and the Petrel manuals if you haven't already.
The Q also says its user rechargable battery is good for about 3 yrs of 50 dives a year. I have no idea what it costs to replace the Q's battery, but I plan on diving my Petrel for more than 3 years and I definitely dive more than 50 dives a year...so I feel pretty good about my 'eats any AA batteries' approach. Another point: the Q has a charger port plug you must have in place when you dive. Seeing as how the X1 and Cobalt have managed to include chargable batteries without such crappy design compromises, I don't see why that was necessary... but yeah, great way to flood your $600 computer there.
Based on an old SB post, it looks like some Q upgrades may be priced as follows:
$50 for profile downloading, plus PC interface cost
$100 digital compass upgrade (just buy the SK7 in a DSS boot FFS!)
See also:
http://www.scubaboard.com/forums/dive-rite/410621-nitek-q-software.html
