Any sport, cap or no cap, teams overpay at the start of FA, which is why the Spurs wait the suckers are weeded out before bidding on players. Lakers will be paying Nash more like 30mil a year to play for them with his added salary. Yeah, Buss must really want to win.
CBA has huge ramifications for going over the Luxury Tax. The Lakers 98mil dollar roster 3 years ago would have cost Buss like 90mil in Tax Penalities and as a repeat offender, make it 120mil. That's right, for being 27mil over the Tax level its $3.5 times the amount over, and $4.5 for repeat offenders.
The Lakers are going to be paying around 45mil + in Luxury Tax with Nash's new salary. Next year, it will be around 60mil. So yeah, it does curtail it when you see how huge the penalties are going to be. Unless your Mob Steel Tycoon from Russia, this will deter most owners from exceeding the cap at extreme levels.