Whilst the 10% fall in guidance is a significant issue the bigger issue may be that the company was maintaining guidance only a few weeks ago. Has business deteriorated massively, did management not know what was happening or did management know what was happening and decide to try and hold the guidance until the gap got too big to pretend that it could be closed? Honestly I do not know nor can I sensibly give an opinion.
In terms of pricing I see the profits warning as requiring a review of the DCF, though many of the shorter term positives, e.g. euro 2016 and the Olympics still remain.
As such price targets have been adjusted to 500p - 750p. The shares are likely to be volatile in the next few days. There has clearly been some retail buying hoping for a bounce. There is also likely to be further institutional consideration of positions. Particularly as SPD may be kicked out of the FTSE 100 in the near future.
Given the above I am likely to add to the position if the price stays below 500p, but am likely to leave this until after the end of January so the price can settle.