Yes, without hardware acceleration CPU load will be much higher.
Since videos have such big number of ReFrames really rare - it's better to switch it on, when your will play other videos. And only if your have such problematic video again (artifacts with hardware acceleration) - switch it off again (only for that video)...
Anyway, it's really easy - you don't have to restart player (like other players like MPC, PotPlayer and so on) - just use seeking (after switching hardware acceleration on/off).
That's why I have a suggestion for Splash - fallback to software video decoding if GPU isn't able to decode stream properly (e.g. intel + big number of ReFrames, or nVidia VP3 with 1024xXXX videos)