Hi Rob,
I took a look into this a long while back so apologies if this has now changed, but the portfolio scenario modelling just didn't cut it for real world resource or financial modelling. (basically too complicated, not quick enough)
With your proposed solution in CA PPM, it does sound like a lot of work and I believe only the plan of record would feed into the PFM modules. Check that though.
The problem stems from the effort into cost generation, which can't be re-run at portfolio level.
In my ideal world we'd have "sliders" where we could control external internal splits of a portfolio role 0%-->100% and see the impact to the portfolio straight from the rate matrix, as this is such a common business scenario. (i.e. project manager role adjusted from 0% to 80% contractor, $800k increase in cost to the portfolio).
I guess we're entering into the fuzzy world of HR and departmental planning, but a very real scenario if you simply don't have the resource to deliver your roadmap.
I've built tools outside CA PPM and would be possible to add into the tool via a custom web app, as long as you have the base data.
I'd love to see "portfolio resource pool modelling" out the box