Yeah, I hear you on the Z-wave costs. I only have like 4-5 zigbee things (mainly light bulbs for fans that don't have seperate fan/bulb switches and 1-2 old SmartThings devices I still use) for the same reasons you mention (WiFi) as well as better range (though less mesh hops). I now have 2 Z-wave bulbs but they were not cheap (like $25 vs $9 for zigbee), I only use bulbs for fans or lamps that aren't on a switch, having physical switch fallbacks is a high priority for me.
What home automation hub are you using? I'm on SmartThings right now (been with them since the Kickstarter) but I've been eyeing HomeAssistant. I have HA running on a Pi right now with the ST integration so that I can play with it without going "all in" and I'm liking it so far. That said it's way more hands-on than ST but also feels a little more stable. I have used SmartApps extensively but always hated how fragile they felt, in HA I might have to look at a YAML file or code but it does what I tell it to do without issue. WebCORE is cool but it also worries me when it comes to long term stability since I don't trust SmartThings/Samsung very much.
