If you use this method, you must also program the serial port to be a high priority via the interrupt priority register
My point above
4) the RI ISR must have a priority high enough to be able to fetch chars well within a character time (1/(baud*10)

There is nothing wrong with NOT having the serial ISR (on derivatives with separate RI and TI interrupt, RI will do) at a high priority if your system is well designed

Let us assume 28.800 baud which gives a character time of approx 300usec. If your other interrupts are so bloated that they upset the need that a request for serial must be accepted within 300 usec, you are in big doo-doo anyhow. So, in a well designed system, there is no need to insist on "a high priority" in most cases. HOWEVER, if there is no way you can have the other interrupts behave (facts, not excuses dear Sir) you will have to adhere to the wording of my point 4).

Usually, if you need fool around with the interrupt priorities for any reason other than "just to make sure" you are in doo-doo due to bad design.

Erik