As it is SPG Lifetime Gold isn't worth much because SPG Gold isn't worth much and there are quite a few other ways, some of them pretty easy, to earn SPG Gold on a year-by-year basis.
Marriott Gold is worth significantly more, but there's no guarantee that SPG Lifetime Gold will convert to Marriott Lifetime Gold -- I think we can all agree that considering the relative value of the two statuses, the current policy of matching annual SPG Gold to annual Marriott Gold is an overly generous move by Marriott, perhaps designed to earn them some goodwill with SPG loyalists. A more equivalent policy might be if they decide to match SPG Lifetime Gold to Marriott Lifetime Silver, which is more in line from a qualifications perspective. But like SPG Gold, Marriott Silver isn't worth very much.
So considering that, I would say it's not worth it to go out of your way to chase SPG Lifetime Gold. If you were 3 nights away or something then yes it might be worth the stretch, just in case. But not if it's going to be a huge investment.