My house was designed from the ground up to be X10 friendly. I get avsolutely no erratic X10 performance. I only use very high quality "X10" devices made by Leviton, I do not use the cheap stuff from X-10. All X10 signals come from the house's home automation system through a wired CM11A. This is a device that takes commands from a PC in serial format (RS232) and issues X10 in much the same way that the IR543AH takes commands in IR format and issues X10.
The IR543AH is just a device, relatively small, that receives IR and puts X10 commands on the power lines. I had used it in the past, but no longer do. my setup is much more sophisticated and involves a PC as the main contol device. Go to my website www.the-gordons.net
and read about the Home theater to get a good idea of how it operates.
If the device (e.g. blind) requires IR, then it requires IR. RF is very "open". There are no standards and every device is different ergo there are no universal solutions.
I had a netx and sold it. It did nothing for me except introduce additional delays. It was less reliable than straight IR.
My house has a Xantech wired IR network with IR receivers strategically located. IR is received around the house and all IR signals go to the PC where the necessary actions are perfomed using X10 or RS232 or IR with any necessary protocol changes.
I do not see a big deal in putting the tiny IR emitters where ever you need to bring IR to, but you have to be willing to run/hide wires. Another approach is in each room have several very powerful IR emitters (commonly called blasters) which bathe the room in IR. This could be IR From the pronto (in another room) if the pronto is issuing IR and you are receiving it and feeding it to IR balsters in the same room, then there will probably be an interference poroblem as the IR streams will be delayed and overlap. That is why many of the IR emitters totally block the receiver/sensor they are servicing from seeing any IR other than what the emitter puts out. Checkout the Xantech line.
Hope that helps