GLM,
First things first; Are the results worth the cost?
We know that the X-boat system is a sham and we also know that any world worth a damn; economically worthy, has any of the various listed bases, occupies a strategic location, etc., is already linked with other such worlds via merchant lines, corporate couriers, subsidized shipping, and naval/scout assets. So, will adding those worlds not already connected by the communication links already in place actually improve things?
Don't forget the "economically worthy" bit. If a world has any trade potential it is more than likely already trading and thus already has regular communication links within it's subsector and beyond. The only world that are the exception to this are worlds that should be trading but aren't; hi-pop worlds with xenophobic governments/cultures that limit outside contacts. 'Improving' communication links with them won't change the trade picture one whit.
Next, look at the cost involved. The X-web described in TNE's 'Regency Sourcebook' had a stated goal of each world recieving a message 'boat' from every world within six parsecs. Your question limits the radius to 4 parsecs but the number of vessels involved is still extremely large.
To reach our "one boat per day" we'll need seven boats per jump. A jump last 168 hours or seven days. You'll need 7 boats in each and every 'pipeline' between worlds to achieve your "one-a-day" rate. And remember, you'll have a two pipelines between each world; a "Send To" and a "Recieve From".
Look at Ffudn/Glsiten. That system has twenty two worlds within four parsecs. That's forty four 'pipelines' and 308 'boats' with no room for mishaps, misjumps, or maintanance. That's over three hundred boats to 'wire up' one system to an X-web.
Simply do the math I just did for entire subsector to find out how many boats you'll need. Then multiply that by the cost of an x-boat. (Don't forget the volume discounts!) Now look at that number and ask yourself if it can be afforded. Remember, you've haven't even figured in spares, salaries, maintanance, tenders, or a host of others yet.
Will trade be effected? No. Any world that can/wants to trade already is trading. More communications won't change that sustantially.
Can a local noble afford to susidize it? No. The cost far too great, all his other responsibilities would be ignored and he'd still be hard pressed to fund such a huge system.
Have fun,
Bill