Insteon or UPB if controlled by third party RS-232

I am looking to add lighting control to my existing home control system (Elan VIA's with an SC-4). I would like to be able to control the system with RS-232. I am looking at a medium sized system to control a 2500 sq. ft. home. I have narrowed my choices down to either UPB or Insteon, but am not sure which one to go with. Both have there pros and cons but my interest is in the RS-232 control. I hope to be able to directly connect to the systems with either the PIM (UPB) or the PowerLinc V2 Serial (Insteon), or PLM (Insteon) to my Elan system. I have a few questions to compare with each.

1. I would like to confirm that one or both of these systems can be controlled in this manor with or without other add-ons. (If add-ons are needed please explain)
2. RS-232 protocol, where can I obtain this for each system? With the Insteon it seems to get the RS-232 protocol I need to buy there "developer" kit, but is this necessary or are the codes available elsewhere?
3. Which one is easier to work with? (programming, troubleshooting)

Questions not pertaining to the RS-232, but more to interference, I have computers, plasma TV’s, ups’s, A/V equipment racks, and shop with large power tools (230V), which system will be better equipped to handle this. (I know this is subjective) My home is a simple 2 panel box layout both boxes 200amp 230V connected to a single service box. One thing good or bad is all of my lights are segregated from the outlets, meaning all my lights tie to 5 breakers and outlets tie to different breakers. I can easily tap into these light lines and add a few outlets for control devices if it would help.

I would also like to control the shop at a later date. The shop is about 100 feet from the house and as a previously said on a different breaker box, but same main service box.

I pay close attention to both protocols, and here are my personal opinions:

The UPB protocol is not only more mature, but also more straight-forward. What needs to occur on the powerline is simpler (despite the Insteon marketing line that Insteon is reliable because it is 'simple'). Therefore, I feel UPB is easier to code for.

The Insteon protocol is also a moving target, still.

The RS232 communications between the host and interface (PowerLinc or PIM) is at a higher level with PIM (again, IMHO).

As for the PHY layer: I believe that the 130 kHz carrier and FSK modulation of Insteon will have problems in a noisy environment. I have mentioned before that I expect powerline noise to increase substantially over the coming years. For this reason I am not bullish on any powerline protocol, but I think UPB has an advantage over Insteon with regards to noise immunity.

If you haven't noticed yet, I would advise that you go with UPB, at least at this point in time.
I can't predict the future, but at this point in time I would have to agree that UPB is more robust and mature and a better fit. The UPB specifications are fully documented and pretty easy. Configuration has always been a strong point of UPB with their UPStart configuration and test software. As you know, any protocol (PLC or wireless) can be influenced by noise or other outside influences, your only guarantee against is hardwire, but UPB does have a very strong signal and is pretty robust. I do have 1 very noisy electronic cooktop, but the UPB signal even with high levels of noise can usually power thru with a few retries. There are filters available if needed. Also, PCS has another protocol called IPC which is designed for noisy commercial environments, so if you have a large commercial type shop, that may be something to look at as well. I don't know much about it other than what is on the PCS site (see beginning of link above).