Studio lighting: pack/head?

Disclaimer: for tax reasons, I choose to spend a sizeable amount on photography purchases annually. I tend to buy based on the possibility of making photography a serious, high-end business, but don't make money currently on any of my work.

I've got a mix of Profoto lights (D1 500 Air, B1, B2) and I'm thinking ahead to future lighting purchases. I love the convenience of the B2 system and having far less weight hanging out on a grip arm (i.e. beauty dish overhead), but they're a bit weak on power and the modeling light is most certainly wimpy (9W LED, equal to a 50W incandescent bulb). I could put a D1 out on the arm, but that's a lot of weight. I could buy a D4 pack and one or more heads, but WOW that's expensive. (Yes, the Acute packs are far less expensive, but they don't support the Profoto Air system aside from basic triggering, and that's a no-go for me. The overall lack of digital control and "engineering degree" needed to work them just doesn't jive with what I've put together.)

I know that a pro-series pack/head system opens up other features and capabilities: compatibility with a few modifiers that don't work (or don't work right) with the lights I have now, higher power (ability to put 2400ws into one head), brighter modeling light (500W beats the 300W of the D1), shorter flash duration (in many but not all cases), ability to use RingFlash head, ability to use other specialty heads (albeit also expensive).

Any of you go with a pack/head for studio use along the lines of a D4? If so, what drove you in that direction?

Have used a number of products in various people's studios over the years. Profoto, Speedotron, Alien Bees, Einsteins, Elinchrome, Broncolor, etc.
For my own lighting I went with Einsteins. In the compromises of size, weight, power, portability, flash duration, control options, colour temperature steadiness, and cost they were my preference. I work in studio and on locations rather frequently as well using battery packs.
If I was only working in a studio I would have gone with a power pack and heads for the extra output when it is very occasionally called for. As a work around less powerful units can be fired twice for extra light in still shots. The cabling to power multiple heads from one power pack is workable in studio but not so friendly for on location work where I often want to spread out a bit more. Weight and system cost were other major contributing factors in the decision.
Ring flash units are not something I buy as a circular gobo on a smaller octabox, leave 3-6" around the edges, makes for some awesome ring light. Try it on a 60" one sometime to see what it does with a bigger light source. You just might like it.

As a quick follow-up, I took the plunge on a D4 1200 Air and four heads, and couldn't be happier with it. I've shifted into headshots, and this gives me a great tool to visualize the finished images. I did the purchase on Ebay, and one of the heads will soon need a new locking screw on the stand mount, but everything works, and that was my goal.