hey, i've been planning to build a sequencer for a while, and i think i've cracked the dual 4017 nut, allowing for 16 steps. I thought i'd post a rough outline as i've gotten alot of inspiration from your work and website and i thought i'd try to give something back.

the circuit is a hybrid of yours and the unreliable 18-stage led sequencer, with a couple of tweaks of my own.

ok.

the clock source is connected to one input of two AND gates (lets say gate-a and gate-b. I used a 4081 but any AND gate ic will do. The output of gate-a is connected to pin 14 of 4017-a and the output of gate-b is connected to pin 14 of 4017-b. The second input of gate-a is connected to pin 3 of 4017-b, and the second input of gate-b is connected to pin 9 of 4017-a. Both of the 4017 have pins 15 and 11 connected together. Thats it. Pins 3-6 of 4017-a are the first 8 steps of the sequence and pins 2-9 of 4017-b are the last 8. This rest of the circuit is the same as your step sequencer, using another 4018 AND gate to cut the steps and a 4016 as a gate (i've used 9v and changed the resistor values but this should make no difference). 

I have found one frustratingly glitch with the circuit . It locks at both step one and nine when it's clock at very high frequencies. I've found that disconnecting pin 11 from 15 on 4016-b and connecting pin 11 to 12 breaks it out of this freeze. I think capping the frequency below the freeze point would be the best option, and not really a hassle as it is a very high frequency. 

Other than that the circuit seems pretty stable, and better than anything else i've come up with as the number of steps can be changed easily by moving the reset pin connection on 4017-b.