Any disadvantages over a longer macro lens?

I already have the AF-S Micro NIKKOR 60mm f/2.8G ED (minimum focus distance 18cm). However, I have found that I have to get too close to the object. I now want to get the AF-S VR Micro-Nikkor 105mm f/2.8G IF-ED (minimum focus distance 31 cm) because it has vibration reduction and the minimum focus distance is better. Is there any reason to keep the shorter macor lens (other than size and weight) if I'm going to get the longer one - Are there any advantages of keeping the shorter one as well?

Also would extension tubes work well on the AF-S VR Micro-Nikkor 105mm f/2.8G IF-ED? How much closer could I get and how much larger would it make something like a small ant?

First f2.8 is not useful for macro, depth of field is so narrow you will be using f11 or f16.

There are other cheap options, close up filters are cheap >£20 a set on eBay, get the ones the same size as your filter thread. They maintain the lenses connection with the camera so exposure and auto ficus (limited usefulness) still work. Image quality is better then you might expect from such a cheap solution.

Once you start getting into high magnifications auto focus is pretty useless, the depth of field is so shallow it rarely focuses where you want. The easiest way to focus is to move the camera nearer or further away, focusing using the lenses focus ring is no good.

My preferred option is a set of bellows, these have the advantage of being able to alter the magnification, often up to 4X life-size) are much cheaper to buy than a dedicated Macro lens and will take any old lens they have the fittings for (often the old M42, 100's of cheap 100mm lenses available usually of very high quality) You would need an adapter for your cameras bayonet mount.

Everything is against you in Macro, the biggest problems are, first your camera is only seeing the light reflected from a small area which makes the view through the viewfinder dim and difficult for focusing.second the more you magnify the less depth of field you get so focusing gets even more critical. Live view helps here as it will brighten up the dim view, some cameras also offer a magnified view which is extremely helpful.

Being further from the subject is a double edged sword, you have the advantage of being further from your subject so you can get some light in there and you're out of the 'radar zone' of insects that tend to ignore you, but it also magnifies movement, camera shake is a real problem. Because your using a small aperture and the light from the small area your photographing is dim shutter times will be long. The answer to both problems is flash. Nothing fancy just a small manual flash is all I ever use. Flash on low power has a very short duration (less than 1/1000th of a second) which gets around camera shake and enables hand held shots. You can get ring flashes which fit onto the front of the camera, avoid the cheap continuous light LED ones you need the flashes short duration.

My 'bug hunting kit' consists of my DSLR (preferably with live view and magnified view), a set of bellows set to magnification I want that day, a 100mm lens a manual flash with sync cable. I got my kit years ago and it cost less than £50 plus camera.

Everything is manual, I set my aperture f11 or f16, I set my shutter to the cameras 'X' speed which varies according to camera make, 1/125th of a second is good, I take a test shot and alter flash power to get the exposure, now I'm set as the flash to subject distance doesn't alter the exposure will be spot on all the time, the flash duration is short so I can hand hold, all I have to do is get the focus where I want it by moving the whole contraption nearer or further from the subject and press the shutter, results like this every time.

Short answer, no, unless you want to use it as a portrait lens.

Tubes work well on a 105 (I'd save my pennies and go for the tokina but that's just me) your magnification increased but your working distance decreases.

If you do portraits you might want to keep the 60mm for head and shoulders shots. If you really don't want to keep it, try trading it on craigslist