I tend not to glyph renew, but it depends on the situation. For encounters like Blood Queen where there is a raid wide damage aura I don't glyph renew. By not glyphing renew you can keep a HoT rolling on more people in the raid and the more powerful ticks are more likely to overheal.
Glyph of Renew is useful for fights where you are using renew to heal incidental raid damage. E.g. someone takes 8k damage so you pop a renew on them. A glyphed renew will get that person to full one tick (3s) sooner which is useful and you expect the last few ticks to overheal whether you're glyphed or not.
The spec you show is ok, but only if you find you are having mana issues. If I were trying to pick up Mental Agility I'd go with a
spec like this. I couldn't imagine playing a Holy Priest without Surge of Light -- it's a far more worthwhile way to spend two talent points than +2% healing. I'd also shuffle that third point in Blessed Resilience to Healing Prayers. You'll be casting ProM on cooldown so 10% savings works out to roughly 40mp5 which I'd take over 1% healing if you're having mana issues.
If you have a
[Spark of Hope], I'd recommend swapping it for one of your throughput trinkets instead of changing your spec. The spark is a solid 150-200mp5 if you're spamming instants with a good amount of haste. I found swapping
[Purified Lunar Dust] out for my spark was enough to get me through Blood Queen in my 10 man even though we lacked replenishment.