It's weird, I tried to think about where my recovering arm was I started to pull but found it almost impossible to visualise it as I was swimming. Guess that's why being videoed helps.
That was exactly my problem too... I watched the video of myself and thought 'oh, that's a bit messy' but didn't really have any idea what I was doing wrong. Then my coach started hammering on about rhythm and timing but for 4 weeks I just didn't get it. I sort of understood what I thought he wanted me to do and I thought I was doing it, but apparently only for a couple of strokes each length, and never consistently. It wasn't until watching that Hazel video and mine side by side that something finally twigged and for the first time I can now actually feel when I get it right in the water.
I'd seen that Hazel video several times before, I guess you also just need to have that serendipitous coming together of different things in your mind.
I only use paddles and fins in the masters sessions and only for drills, they aren't allowed in public sessions in my pool (even if the lane is completely empty!!!!!) so they don't get much use. Also, I only use kick board and pull buoy rarely and my pool have a stack of them for people to use so I wouldn't bother buying my own.
I think if I were going to spend any money on swimming then I'd buy some coaching time and then maybe one of these swimsmooth.com/finis-tempo-trainer-pro.html I don't have one but it might make pacing lengths easier (swimsmooth.com/training.html)