Re: INS/GPS aren't the only options
Useful so long as you have clear skies.
Pick yourself up a "cheap" (relative term) telescope that does auto-aligning. We've had them since the days of the BBC Micro and some are able to digitally view the image through the scope, find stars, recognise them, track them and align the telescope automatically. You don't even need a modern CCD, like I say, they had them back in the days of BBC Micros and video digitisers. Many of the cheap ones do it via GPS because it's just not worth the hassle, but the older / more expensive ones actually use the constellations.
Now do it on a cloudy night. You're stuffed. You can pay a lot of money and you're still stuffed. And one of the first things you have to do is give it some indication of where on the Earth you are because without that, it makes things a little more difficult. Probably great for when you're above the clouds and trying to find a Middle East country, useless for anything when you come below cloud cover or near to your target (i.e. within 100 miles). Not to mention that you have to keep a sensitive camera pointed at the sky all the time from your ICBM which is a difficult but not insurmountable task in itself.
I reckon it may well be used in combination with other things, but you really can't beat a decent GPS signal for the last stretch. The only thing about astronavigation is that generally your enemies can't control / block the weather any more than you can.
And in terms of accuracy, I'm not sure I'd want the error from software recognising constellations through a CCD in a warhead. Certainly not if you want to pinpoint-bomb something like a bunker. Think how well your computer recognises QR codes or shops recognise barcodes "first time", and then strip out all of the error correction inherent in the system (stars in the sky are not arranged modulo 13, or have an ECC built into their patterning).