A special dividend can be a useful hard power play in combination with other hard power plays, but, by itself, it will only make it easier for Valeant to win.
Valeant, with junk bond status, can borrow about 4 years worth of profits. Furthermore, by shutting down R&D and getting rid of most Allergan employees, Valeant (at least in the short term) will be generating a lot more profit from the Allergan products than Allergan will. This is how Valeant is able to borrow $72 per Allergan share to finance the cash portion of their offer. Allergan, with top bond rating, and requiring shareholder approval to reduce it's credit rating, can only borrow, maybe, 2-3 years worth of profit -- or about $20-30 per share.
Therefore, if Allergan were to borrow $20-30 per share and hand it over to the shareholders; Valeant will simply reduce the cash portion of their offer by an equal amount and continue with their effort as if nothing happened. The Allergan shareholders will still be getting the same amount for their shares (between the Valeant exchange offer and the Allergan special dividend) and the total new debt will still be the same (between the borrowing Allergan would have done to finance the special dividend -- to be inherited by the acquiring Valeant -- and the borrowing by Valeant to finance the cash portion of their offer). Effectively a non-event -- except that it will take away all the borrowing power Allergan could have otherwise used for other hard power plays (such as acquisitions) -- thus making Valeant's life easier, not harder.
(The same applies if Allergan were to use borrowed money for a shares buyback. Valeant will have less borrowing power, but will also need to buy less Allergan shares, so they will be able to offer substantially the same deal -- but with a different cash/stock mix -- and end up buying as many shares as before using about the same debt and equity as offered before)
All that said, there is an available play along the lines of special dividends. I don't think it's an attractive play (because it will seriously damage the surviving Allergan), and I don't think management will seriously contemplate it (for this same reason), but it is an available play: The play is to "out-Valeant" Valeant. Specifically, borrow even more money than Valeant is prepared or able to (say, $140 per share); reducing Allergan's credit to the bottom of the junk category (even worst than Valeant). Possibly do more cost-cutting and/or divestitures to finance that amount. The shareholders will need to approve, but shareholders almost always vote to take cash. After that, Valeant will only be able to acquire Allergan on a straight shares-for-shares exchange (no cash), and Valeant's own credit rating will suffer if it were to assume Allergan's new huge debt. Even if Valeant doesn't walk away (or forced to walk away by the covenants of their current lenders) from the now toxic Allergan, the Allergan shareholders (with the cash securely in their pockets) will see no reason to exchange their shares of heavily indebted Allergan (but run by a management team that knows how to monetize the Allergan products) for the equally heavily indebted Valeant (who may or may not know how to run Allergan's business -- and if not, would be a short walk from bankruptcy wiping out all shareholders).
Dan.