Under the current system, the TSP contribution isn't matched by the government, it's really not a benefit at all. 5% matching is a huge benefit (that I believe is) offered pretty commonly in the private sector which we don't get under the old system (because a 50% non-contributory pension is such a good deal and very expensive to the government all by itself).
One benefit I haven't really seen discussed (didn't read all comments) is the very cheap expense ratios for all the TSP funds AND the fact that you can put 18K into your ROTH and STILL fully fund your 5500 for each of you and your spouse in a ROTH IRA. $29,000 a year into a tax advantaged ROTH growth situation that can REMAIN in at the low expense rates until you choose to move it or use it...pretty good in MY book. 4% and do that over 5 years and you have $160K+...obviously not applicable at these levels for the E-3, but very doable for the O-3+