Hey Nick
Google have thrown their hat in the ring here and stated that responsive design is preferred, probably due to the reasons you are stating that people could start to try and play silly games with only rendering specific content for specific devices, but, as with everything SEO, I would not worry about that if you are not looking to cheat.
The article is here with further reading linked out:
http://googlewebmastercentral.blogspot.co.uk/2012/06/recommendations-for-building-smartphone.html
& here
https://developers.google.com/webmasters/smartphone-sites/
They basically state that it depends on your requirements, as it always does but in order of preference they want the following.
1. Responsive Design
2. Mobile site on same URLs with containing 'equivalent content' - now this is important as if I serve my mobile site, the main piece of content is the same, but some of the widgets are dropped, but this is just extras and the main purpose of the page, page title, URL and everything else is the same - the page is a parred down equivalent for mobiles.
Alternatively, you may have a completely different site for mobile users but this is not really the route you want to take in this smartphone driven world.
If you did want to test this and make sure you were not going to run into any problems you could simply set up a wordpress site with some supplemental text widgets and then use the wptouch plugin to show trimmed down versions of the content on the same URLs. This will give you a test environment you can rig up in a couple of hours max and you can put your mind at rest.
Give me a shout if you need any help!
Marcus