If you're happy with your results, why block anything in Robots?  The short term answer is tags are working for you.  The long term answer is you're creating duplicate content.  So it just depends - are you optimizing for today and tomorrow's sales or for long term success.  There is no "right" answer to that but that's the question.

You don't want to index tags in Wordpress.  You'll have duplicate content on any post that has more than one tag on it (which is almost all of them.)   You want to get the canonical permalinks indexed and that's it.  Search for a post you have indexed under a tag and then do a keyword search to see if it appears a few times (archives, multiple tag pages, etc.)  That's bad - you want to fix that.

I block wp-admin and wp-includes just because they don't need to be indexed.

As far as tags, you can easily no-follow all of those with any half decent Wordpress SEO plugin like Yoast or All in One SEO.  I would definitely noindex them.

Cache won't be built or updated overnight so sometimes the first few caches are a waiting game.  How long has this site been live?  If it's fairly new, what you're experiencing is common.  If it's an older site and you recently started changing a lot of the technical stuff - redirecting, canonicals, etc. it may just take a little while to settle in.

The other major recommendation I would give you is to change your sitemap "change frequency" to be slightly more accurate.  Does this page http://www.fuchia.co.uk/products/clothing/dresses/dog-tooth-print-dress.aspx  really change "daily"?   By having daily on every page you aren't helping Google prioritize their crawl, which means you may get a cache for your dog tooth print dress before you get a new cache for your main page.

So I would fix that, resubmit sitemap and then it's a waiting game.  Could be a week, could be two, I've seen it go almost a month but not if you use G+.

I've found that if you manually ping Google, they often update their cache at the same time.

Google doesn't have a cache for either cache: www.fuchia.co.uk. or cache: fuchia.co.uk. so I don't think it's a canonical issue.

I would suggest a few things:

1. Use PingDevice http://www.pingdevice.com/

2. Put your main domain in a Google Plus post every now and then.

3. Resubmit a sitemap.  Usually this gets you crawled fairly quickly and possibly updates your cache.

Fantastic, fantastic post Ryan!  Dealing with this for a client now - good info!