Both are great domains - I presume you've checked the numbers? The new Google tool, seems to give Photographers 14,800 local exacts at a cpc of £1.68, while Planners gets slightly less searches 8,100, but a slightly higher cpc of £1,78.
The trouble you may have trying to get a high value end user sale is that both of them (but especially the photographers) tend to be fairly small, local operators, who trade on reputation and word of mouth. And there are only so many weddings a year that each photographer can cover.
Planners might be slightly different, and presumably generally only get called in when there is a reasonably large budget. As such, they have control of or at least influence over significant sums of money and may be able to justify correspondingly high fees. For them, attracting one extra commission, might make it worth paying a healthy amount for a niche defining, generic domain. Inevitably, the trouble might be finding someone with the belief, understanding and most importantly, budget to pay well.
For both, it would seem very likely that London based firms are the ones likely to have the level of competition and fees to make one of these names a sound investment. But they might not be easy to find!
Alternatively, I guess some sort of directory site, with either commission, or paid adverts might be easier to scale up and monetise, with a long term income stream a good possibility.
Whichever route you go, I have partyplanning.co.uk that might add to the stable nicely ;-)
Now... how about someone putting their head above the parapet on my .me.uk name?!
