I'd be tempted to leave the topping-off for a while. Unless you're going to rake it all up,it could cover the new seedlings coming through and kill 'em off,that's if they survive a couple of ton rolling over them too. If you let the older grass set seed,it'll spread naturally and hopefully sprout soon too. My field's pretty much the same and I have left the old seed heads on,but I do go out every evening for an hour with a scycle to keep the thistles down...Ree