"You give up the iconic spellstrike feature in exchange for the ability to attack an extra time per round, which you could already do with spellstrike anyway."

Well the idea is that if you're going Spellblade, you'd be dedicating yourself to a TWF style, and therefore you'd be getting more than one extra attack.

While I agree that Spellblade is a small step down I think you're being harsh. What it is, is situational - if you optimize for a TWF style (e.g. GTWF + Piranha Strike) it can be pretty beneficial, i.e. letting you contribute to combat while conserving your spell slots and pool. You create the athame, buff up and go to town in a large combat without casting anything further unless you need to. The athame is a free ghost touch weapon that ignores DR as well.

Spellblade Parry is worthy of note because it boosts your touch AC and CMD as well. My main issues with it are that it won't stack with other deflection bonuses (so if you get deflection elsewhere it's useless) and that it doesn't apply to ranged attacks/rays for no good reason.