Since radioisotope thermoelectric generators (RTGs) operate by turning the flow of heat into electricity, and Titan's atmosphere can absorb heat faster through conduction than a vacuum through radiation, would an RTG (or a set of them) produce enough power on the surface of titan, say, for a manned base?
RTGs would be far more effective for the reason you describe: the job of a large radiator could be done with a small heat exchanger, and a larger heat exchanger could get the cold side temperature much lower. Taking the MHW-RTG used on the Voyager missions as an example, the cold junction temperature is ~600 K, an RTG designed for Titan could get it much closer to 100 K.
However, the MHW-RTG already has a Carnot efficiency of (1273-573)/1273 = 0.55. If you redesigned the thermocouples to keep the same hot-side temperature while the cold-side was dropped, you might get that up to ~0.9, but you aren't going to even double the electrical power output, all else being equal. Even if you improved the conversion efficiency independently of the Carnot efficiency, there's only ~500 W/kg of thermal power to work with. You can get a healthy boost to the power budget of a rover or something (provided they don't need even more for heating), but RTGs are still not a good option for heavy power demands like keeping a base running.
would an rtg (or a set of them) produce enough power on the surface of titan, say, for a manned base?
Maybe, but you've forgotten something fairly important.
That very cold, highly thermally conductive atmosphere that's boosting your Carnot efficiency is also going to be sucking a huge amount of heat out of your manned base and all of your surface equipment.
Moon rovers like Lunokhod 1 had to survive the chilly lunar nights, which get down to 140K for a couple of weeks. They used host radioisotopes not for power generation, but to stop them freezing to death, a risk even for electronic equipment at that temperature. The average surface temperature on Titan is under 100K... that's quite significantly colder.
Your base is going to need some pretty significant insulation and plenty of heating especially for anything that ventures out of the main insulated bubble. The savings you make in terms of heat engine power generation are likely to be offset by heat losses from everything you'd like to not die of cold.
It is also well worth remembering that the power density of RTGs isn't great, and their lifetime isn't amazing... their output drops continuously during their life, too. They're great for deep space probes that have to be launched from Earth, because engineering an economical compact lightweight nuclear reactor is a pretty tall order, even without the environmental concerns (real or otherwise) of an accident.
If you can drop an entire habitat on Titan, you won't be mucking about with short-lived RTGs coughing up a disappointing and shrinking amount of power, you're going to send them the real thing, because they'll need it.