Regarding paying back the loan with 'After tax' dollars, the only 'after tax' payments you are really making is the interest on the loan. The principal, lets say $10k, is being paid back with the SAME 10K you were given as a loan.
The fact that the interest is being paid with after tax dollars is really inconsequential, because ANY loan you get would be paid back using after tax dollars.
The real question is simply, is your expected rate of return in the TSP better than any expected savings you get by taking the loan out from the TSP rather than from another source. If the TSP loan is your only method of securing a home, then of course the amount of savings is secondary to how much you want a home.
The fact that the interest is being paid with after tax dollars is really inconsequential, because ANY loan you get would be paid back using after tax dollars.
The real question is simply, is your expected rate of return in the TSP better than any expected savings you get by taking the loan out from the TSP rather than from another source. If the TSP loan is your only method of securing a home, then of course the amount of savings is secondary to how much you want a home.