The general rule for this when it comes to SSRs is "no."
The long answer is "noooooooooooooooooooooooooooooooooooooooooooooooo ooooo." Only apply the long answer when it comes to P2W Eidolons.
I'll have 21k Jewels for SSR Cybele ready, but am I going to find her? I'll have ~11% chance of that, and ~2.5% from guaranteed SSR. In other words, nooooooooooooooooooooooooooooooooooooooooooooooooo oooo.
So, spend your Jewels however you want. Honestly? Isn't not going to have any impact. RNG is going to RNG something your way, or it won't.