IMHO you are trying to re-fight the last war and the Phillies circumstances aren't at all the same as they were back then. The problem with the demise of the golden era seems to be that we established a home-grown core, and stuck with it too long as it aged out, with the only significant additions being expensive, older players we traded for and signed in FA. We were constantly scraping against both the salary cap and the budget set by ownership, yet every hole/problem was solved with another vet. If the farm had been productive and we had rotated out (traded) pieces of the core as they aged and replaced them with good young talent from the farm, or if we had filled holes from the farm, then the cap/budget problem would have been avoided.
Today is nothing like that. We are not anywhere remotely close to the lux cap or what the owners can/are willing to spend. Not in 2018 and not possibly over the next several years. Yes, I agree it would be a terrible thing to build an old, expensive rotation like the one we had, but signing a 30-year old pitcher to a multi-year deal now is not the problem that it was back then. Why? Because we don't have any other 30-year old SP in the rotation. We don't even have any upper-20s SP in the rotation. In fact, apart from relievers and Santana, we don't have any 30+ players we are counting on. It is a very young and very cheap team, the second lowest salary budget in baseball.
The way you run into salary problems in the future is the way we did back in the golden era. You wait to add FA/trade talent until your young core is virtually set, you let the core go old together, and you patch with vets. How to avoid that? Have a range of ages on the team. A FA pitcher we sign now can be gone after 4 seasons, to be replaced with a young SP from the farm. If the rotation is all from the farm and grows up together and gels and stays together, that's great for the short term, but before long you have a starting rotation of all 30 and 30+ guys.
Yes, it is best to grow your own pitching. Fortunately, our roster of position players has come together faster than expected. It is doubtful there are 5 good SPs for this season among our kids. If you wait for the guys in A-ball to fill the gap, then you throw away at least two more seasons. Nola, a plus FA SP still leaves 3 other kids in the rotation, and during the course of the season, it won't be the same 3 kids. We love our young pitchers, because they are our own minor league products -- at least for final development after trade acquisition, but they weren't all that good last season. There is promise and some will break out this year, but it is next to impossible that 3 of them will break out this year. None of them is a top 100 prospect in baseball.