... I started collecting vintage Casio keyboards. I know this because I just got an automated message on Ebay saying it's my one year anniversary with them.
I like them better because they have the old mixed square wave* tones vs. the plastic-sounding samples of the newer romplers. The so-called "consonant-vowel synthesis" faded one waveform out while fading in a second waveform.
I did finally break down and buy a modern CTK series General MIDI model with the learning functions though, for the sake of completeness.
My main vintage instruments were actually professional grade for their time. The FZ-1 was the first 16-bit sampler ever produced. The phase distortion synths competed favorably with the Yamaha DX series (and reportedly infringed on Yamaha's patents). The Spectrum Dynamic synths modelled traditional analog synths and had analog filters and some cool harmonic manipulation thing going on.
* Believed to be based on Walsh functions by some collectors.