I am building my first full spontaneous caster (oracle) and am trying to plan out feats for higher levels. I am leaning towards penetrating spell since the hope is to have high enough knowledge scores within the group to identify SR before I cast, but I'm not sure if the +1 spell level is worth an extra +3 caster level check
Spell Penetration + Dweomer Essence Should be more than enough to get you through. Neither will increase the casting time like the meta magic will and some of your spells may not even have SR.
Heck you may just get by with the Essences. I tend to take Craft Wondrous item on my spell casters to make my gear cheaper. Since the DC is just +5 more for not having a requirement the DC is still low enough to be good at crafting.
I assume you mean the Piercing Spell metamagic feat? (Penetrating Spell looks like something 3rd party which doesn't relate to SR).
For a spontaneous caster, as a rule I definitely like the metamagic better than the basic Spell Penetration feat. If you're reasonably confident you can predict what enemies have SR, boosting a spell by an effective +5 vs SR when it counts is much better than a static +2, even if there is a +1 level adjustment and increased casting time.
Once you get to higher levels, where SR is more common, it might be worth considering using a rod, rather than the feat. At higher levels, the cost isn't overly prohibitive, even for a standard rod (for spells up to 6th level).
Also consider using Dweomer's Essence in those situations where you really need the spell to stick. Not cheap, but very handy in a pinch.
I am leaning towards penetrating spell since the hope is to have high enough knowledge scores within the group to identify SR before I cast,
I would just caution you to make sure this is information the GM is going to make available. By RAW, the GM decides "a bit of useful information" for meeting the DC and "another piece of useful information" per +5 over the DC.
A lot of GMs handle this differently.
Personally, I like the spell penetration so I don't have to worry about which spells I am casting on who (at least due to SR), especially since knowledge isn't going to help you with the "evil human cleric with spell resistance up" kind of situation.
For spontaneous casters though, the metamagic feat does have an advantage, I think.
With a Spontaneous Caster and Meta magics YMMV.
There are only a handful I feel is worth using feats on. Sometimes you can not use a full round action as movement is necessary for many reasons...Survival being a big one.
I personally only like: Intensified, Extend, Rime, Empowered, Dazing, Heighten, Persistent and Quickened. And I typically do not have them all in the same build. I get some (Extend mostly) on a rod (Still a Full Round action BTW). I tend to grab the most relevant to the build I am going for.
I prefer Spell Pen + Essence because both accomplish what Piercing Spell Does (actually comes out better). But does not eat your action economy and still comes out costing a Feat.
Neither approach is wrong. It is more a player's play-style and experiences that really shapes how a player feels about either. I tend to favor Prepared casters more but have played my fair share of Spontaneous classes. Meta Magics and spell selections are different between the two types of Casters. So maybe I value action economy (loss of a move action) more than other players out there.