London Marathon take 3.......?

So its that time of year again, the last long run is done, the taper is well under way, the expo will be opening tomorrow and then the streets of London will be filled with excited runners clutching their race packs.  I am of course talking about the Virgin London Marathon.  The build up and excitement is all part of this huge race.  Only this year I'm not part of it.  Or so I thought.  I still have the option to race and had decided not to due mainly to the recovery taking too much out of my cycle training.  I have enough long runs under my belt this year to make me slightly more confident about Transalpine and running a flat road marathon wouldn't really benefit me much right now.  But then I went for a lunchtime run along Embankment and saw all the barriers going up and started to reminisce about the last time I ran this section of the VLM and what a great race it is.  And its made me want to do it.  To the point where I am convincing myself (and others) that its not such a crazy idea after all.  I could run it slowly.......I have a weeks training in Lanzarote coming up in 3 weeks (thanks to Neptune Collognes!) where my cycling will take precedence for 4/5 days......I was planning on running 66 miles in a couple of weeks which I've decided against so really its a much shorter version of that.........and anything else I can find to throw into the "for" argument. 
The "against" argument is also convincing, and if I were sensible, I'd let that win.  It WILL take too much out of the other training.  I DONT need to run 26 miles on road at this point in my training plan.  It could lead to an injury (all my long runs this year have been off road) which could jeopardise other races/training I've been working towards.  Is just wanting to race really enough to ignore all of this? 
During my run today I thought about letting the weather decide.  If it was too wet to go out for my long bike ride on Saturday, I would take it as a rest day and then run on Sunday.  I have a few days left to think about this and try and recruit some more members to the "for" party.  I like to go with the majority.   Until then I will try and stay away from the Embankment.........