The availability of Stone will also influence our planning, since with it the Pyramids become a feasible build and arguably more attractive than the GLH if we are bulbing heavily. For a Philosophical leader, the number of specialist turns required to generate a GP are as follows:
GP1: 17
GP2: 34
GP3: 50
GP4: 67
GP5: 84
GP6: 100
GP7: 117
GP8: 134
Assuming that the first GP is unaffected by the Mids (being used to bulb Mathematics) then the value of the Mids will be determined by GSs #2 and onwards, the final number being dependent upon the hidden objectives/overall trajectory of the game.
Beyond Maths, a minimum bulb path to Astronomy and Engineering would need 4GSs (Optics, Astronomy x2, Engineering) and .75GS for a GA (assuming this is generated in a wonder city, with 12GPPs per turn coming from specialists, and 4GPPs from the wonder).
4.75GPs: 310GP turns = 930B
The return here is not phenomenal (say Stone + OR = 930B / 223H = 4.17), but this will research Machinery and another tech for us. Since we will likely be the team dictating the tech path, we should be able to start warring 35 turns sooner, while also switching into Police State for cheaper warring. I would say this already outranks the GLH, which can then be captured.
The need for further GPs (e.g. one leader has three hidden objective necessitating Physics/Biology/Electricity) increases the Mids value:
5.75GPs: 423GP turns = 1269B
6.75GPs: 553GP turns = 1658B
And so on. The actual beakers will be a bit higher, assuming we have at least one Library in the capital (and maybe more, given Pericles' traits). In a game where we generate 8 great people in total, 1658B / 223H = 7.4, which is a good return.
Anyway, this is mostly speculative at the moment. Without Stone the value of the Mids plummets.