Saber worth the IVs? Or more summons?

Whether it's worth your orbs would be a question of your goals in the game and how much you like Saber as a character and combatant. Some considerations:
- He's sharing 3% with three other units, and he's red, which means you're getting very poor odds of finding him, which means you can expect to fork over a lot more orbs.
- I personally think there are plenty of units more effective than him in most game modes. In assault modes, it's easier to go with a lot of TA and breakers and anti-type weaponry; in arena we need merges; AR requires very specific play which I think is quite difficult for him (also, Veronica is a huge problem for him), all of which leaves general PvE, where he's OK but a lot of other units are as good if not better. So at the very least I wouldn't go hunting for a better IV.
- I wouldn't look at him from the perspective of how much you've invested in him; I would look at the skills you've inherited onto him as options, and if you like them then you go with them.
- With steady posture, even with the special refine, his spd is kind of in the middle of nowhere. (Also, spd/def bond from Ethlyn was probably a better go. Steady posture locks him to enemy phase, where it's not hard to have the bond active anyways. Quan is a very good unit, so you foddered a really good unit for someone extremely hard to merge.) I think you need to make a decision, whether you abandon this line you're taking with him, or whether you push through with it and get his spd to a level where fast units might not be able to double him, such as using the build I show.
- With spd bane I'd say he's too slow for shield pulse builds without QR. It will be too easy to double him and leave his shield down for the next fight, which means he loses the extra stats.
- if all else fails, give him TA, swordbreaker, bonfire, and refine the slaying edge for def (not the Golden Dagger, in order to save dew), and you have a unit that will wreck 90%+ of swords (because some faster swords will also use swordbreaker) and draw against the rest while making axes cry.