Mega Bucks are a huge help to those successful capitalists! Once you've saved up a pile of Money, head to the AdVenture Menu and hit the "Currency Exchange" Button. Just to note, inflation is a little out of control on the galactic currency front; you might see a quick spike in currency exchange rates. Sorry about that!
Once you have some Mega Bucks, go to your Currency Exchange and click on the Mega Boost icon at the top. You can then purchase some Mega-Boost Tickets. Once done, go to your main investment screen on either planet and you will see your currencies at the top. Click on your Mega-Boost Tickets and you can then select one business to boost with a permanent 777% bonus to profits - that's permanent with a capital "never goes away". You can boost several businesses but Mega Bucks get mega expensive so choose wisely. Once you have boosted every Investment on a planet, you get the option spend Mega Bucks on Platinum Boosts for even more multipliers, so be sure to save some of your Mega Bucks.