Well it depends on what they change in the magic rules. If they keep the basic idea of powr and dispel dice, books wouldn't neccesarily need an instant change. But remember there was ravening hordes after 6th ed came out, a small booklet that gave basic updated rules for all races so they were at least playable until they got a full book.
Again with the units, not neccesarily. Like you say, a unit of 25 saurus is very expensive. They are expensive because they hit damn hard! A lot of their combat res will come from kills, not static. I would wager a unit of 18-20 saurus would have no problem with say a unit of 30 skvane clanrats, even if they got extra static combat res for 2 extra ranks. In many cases, two smaller units will be better than one larger unit, due to the extra movement and manouvrability advantage. Remember, as soon as you hit a unit's flank they lose all rank bonuses and you get +1 for a flank charge.
