On the spur of the moment, I bought a Moog Sub Phatty. It appeared in the classifieds here and was "local" to where we were at the time. It turned our 5 hour journey home into an 8 hour journey. My wife is extraordinarily patient. I had been thinking about a small, monophonic synth for a long time and realised that the asking price was less than I would expect to spend on a bass. I have been messing with synth pedals for years, but this showed me that there is a reason keys played bass sounds different. Having all the controls in one place and accessible immediately has made playing and manipulating it very easy. Don't get me wrong, I am not doing Stevie Wonder bass (more is the pity) but I can do what I want with remarkable ease. It is SO much easier than doing a poor imitation on bass guitar.
Am I going to keep it? I am not sure about that. Now that I have experienced it, I suspect that a midi keyboard running into Logic will provide all the synthy goodness I will ever need. But it is certainly my best ever impulse purchase.