don't waste your monkey money on spec. agents. they're a one time thing, and if you lose your game instead of winning it, you'll have lost a good amount of money. the same goes for the items at the beginning of the game. I know because i've played it past rank 70 on ninjakiwi.com. spend you monkey money on the specialty buildings. they're permanent and can give sweet bonuses to your towers. choose wisely though, you can only have one building activated at any one time. + so others can see this.
it's a dumb idea to give you the suggestion to buy stuff at the beginning of the game because people usually play to get monkey money in the first place. why would i pay 200 some odd monkey money for a one-game feature when i'll only win a tiny amount for that game?