This is ONE OF 3 responses to VC 26 Roger 4 ("New Thoughts")...
I don't know if taxing larger homes would accomplish all that much. In a sense larger homes are already taxed at a higher level (a larger home, and especialy more land, generally means a higher assessed value, and property taxes are based on assessed value).
Cost is not the only issue when someone buys a home. People pay for views, school districts, proximity to work, and other conveniences.
I don't think the problem of homeless will be solved by building homes to the size you recommend. New homes (townhomes and condos) in the 1400 sf range still cost well over $200,000 here and rent for more that $1,200 per month. Those kind of prices are still not in reach of the homeless here in the Bay area.
The local redevelopment agencies are trying to address a number of problems in the south bay when zoning land for development. They try a number a things like mixed zoning (mixing residential with light industrial and commercial) to bring homes and jobs together, thus reducing traffic. Rezoning commercial and light industrial to residential to accomplish the same purpose. Designating many areas close to downtown as medium to high density residential (16 to 32 dwelling units per acre). And zoning areas along the new freeways that are being constructed as medium to high density residential - hoping that these homes will be attractive to people desiring a relatively easy commute to work.
I don't think concerns about the homeless will drive housing construction policy, at least in areas where housing is very expensive. However, I do think that sound policies by city and county planners to ensure medium and high density residential construction close to places of work, downtown areas, and main traffic arteries will serve to reduce traffic congestion, energy consumption, and pollution.