I've seen at least one comment in this thread indicating that the only purpose for which the internal UART is used in his system is for debug. I've seen that sort of thing quite a bit, but, if you need the UART, or UARTs, you can't debug your firmware if the tool you're using wants to use those resources. That, I suppose, is a good argument for a JTAG or other sort of emulation tool, but not all MCU's support those.
Then buy an ICE. And if that is out of the question use a JTAG processor. There is a full complement of derivatives available with JTAG, maybe 1/10 of one percent of apps will need a configuration where no JTAG device will do. The higher cost of e.g. a SILabs f120 development rig ($75-$149) will disappear instantly when you fix the first bug (assuming you make a decent hourly rate).

No, I am not incapable of fixing bugs without an ICE, but I find that the ~$1500 for e.g. a Ceibo is very cost effective. Fortunately I have been able to hustle a few for free, but those I have bought have been worth the investment.

Basdically my attitude is: buy an ICE or use a JTAG chip. I see no case where anything else makes sense.

It is published all over that a developer uses more time debugging than developing and here is an instance where you really can get a solid return on investment.

Yes, whomever manages to develop and debug something without a full set of tools can be very proud of his/her technical skills, but they sure can not be proud of their financial skills.

Erik