It may well be that a fair chunk of the Gold Leaf money (as well as later sponsorship) somehow found its way from "Team Lotus" to "Lotus Cars", depending on the financial health of the sportscar side at any given moment. I read an extract from the recent Chapman biog that explored the ways in which Colin would, from time to time, manoevre funds from company to company to maintain an illusion of solvency!
And the amounts of money were much less, since F1 didn't have the same sort of marketing potential as it does now. Yes, you could possibly get your name prominently in the newspapers if your car won the British GP - but you may as well just take out a newspaper advert, which is guaranteed to be printed whether you win or lose!
For example, Walter Hayes of Ford paid just £100,000 in 1966 to cover the development and sponsorship of Cosworth's DFV engine. Not a bad investment really for 155 GP wins...
Those teams who could get long-term sponsorship deals (McLaren/Marlboro, Lotus/JPS, Brabham/Martini) were in a stronger position as a result, but by and large they were the teams who were already winning anyway. Sponsorship did fuel a surge in the early-to-mid 1970s of chancers who fancied the idea of being in F1 but their wealthy backers soon got bored of not winning, and these teams seldom lasted for more than a season or two (Frank Williams' operation perhaps being the exception through sheer stubbornness on his part!)