Thanks for all the suggestions everyone, appreciate this.
A small correction: Buying a new summon with point costs 16x1800 = 28800 points, while pulling a duplicate of the gold summon gives 4000 points, so thats about 25k points lost.
I'm more inclined towards power as well. So far, have 5 gold summons - Gamaken, Serpent, Dog of hell, Eight span bird and Fukurokomaru.
Over the span of 5 months of playing, have ac*ulated like 40k points now. Guess I'll go for the runes then.
Only reason I'm hesitating now, is because there is a 4th summon tab now. Giving runes to this new slot will obviously be better, but we don't know when it will be available.