I find that the _domestic_ economy just never gets to the point where you are not losing money every turn. Add in the imperative need to sink money into espionage (which does _nothing_ to make you money, given the mechanics) and you can only grow if you're willing to build things at a glacial pace.
OTOH, if you allow tech trading, you can grow your economy rapidly with influzes of foreign capital. That is, max everything that improves your Research value. Keep spending at 100%. Split spending 20% military, 20% social, and 60% research. Focus on techs in the yellow: Trading and Diplomacy. Also crank out any tech that you can complete in under 5 weeks. Then, whenever your bank account is about to go into the red, go to the Diplomacy screen. Contact _everybody_, one after the other. Offer to sell any tech that is NOT weapons, Trade, Diplomacy, or improves research, ship speed, or production. Things like Sensors and planetary improvements. Pick the lowest value tech you can find that fits that criteria, then offer to sell it to every other race.
If you've built up your Trade and Diplomacy values, you should be able to sell that low-value tech for anywhere from a few hundred to a couple thousand bc's to _each_ of the other races. Avoid the temptation to buy techs that others have but you don't. And if you hit on a race with a shallow bank account, make up the price tag difference with Influence.
I find that this strategy allows me to keep my economy running at 100%. And the longer you do that, the faster that you'll build up an inventory of salable techs. Every time I go to market, I usually come away with 10-30,000 bc's in my bank account.
Oh, if you do focus on research (with the 20-20-60 split), you'll want to colonize plaets as fast as possible. Every new planet settled with 250 colonists immediately adds 7-12 research points.
If you find yourself in a bind because you suddenly need warships _fast_ or something of the sort, switch your economy split emphasis to military or social for a turn or two. But remember to switch back to the research emphasis ASAP.
Anyway, I find that this strategy works quite well for me. (Don't know what I'd do if tech trading was turned off though.