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Actually it is quite an added expense for most situations. A converter station is far more expensive than a transformer. Note also that practical DC circuit breakers for higher voltages are not available so the switching flexibility of the "grid" isn't there for DC. Note that HVDC systems are used to connect AC systems where a) end to end where distances are long enough to warrant the increased station costs vs the reduced line costs. b)Ties between areas where stability problems may occur. c)ties between regions at different frequencies. Note that in all cases the links are between AC grids. What makes the AC grid possible is the ease of changing voltage levels with simple transformers and of switching. DC is a bugger to switch. Now as for household use, 48V is low for many applications. A 1200 watt toaster would require 25A DC (roughly 70% larger area wires =$). The problem of breakers is much more difficult for DC (i.e. $$$). Take a look at a simple toggle switch as used for many applications. Compare the AC and DC specifications -provided that the switch can even handle DC- most household switches intended for 15A AC would simply not handle even 2A at 48V and simply arc -not desirable unless you are into whole house heating . Frankly, 120V 60Hz or 240V 50Hz, is nicer to handle and safer in many ways than 48V DC at the same current.
Example: at 120V AC, opening a 5A current with a knife switch causes a small spark. At 120V, 5A DC, the same switch can be opened 1/2 inch, causing a hot sustained arc (possibly 3/4 inch to 1 inch long), sufficient to light a cigarette or anything inflammable nearby). 48V is a bit better but at higher currents - the arc will be heavier.
You suggest inverters. Fine, but your inverter can cause problems with your neighbor's inverter and what you suggest is an added lossy component which has a poor cost/benefits ratio for most household uses. Why put in equipment that provides no gain in any sense?