From what I understand instant coffee is just brewed coffee that is then spray dried and collected. Basically you are just rehydrating a cup of already made coffee.
You can find some very good instant out there if you look. I am trying a can of instant Percol Black & Beyond Espresso this month, as it has been released recently. I normally buy real double espresso from the cafe but have cut it to one in the morning and then instant in the afternoon. Saves me £1.50 a day.
Instant coffee contains more soluble fiber than espresso or drip. Germany has a terrific instant coffee called Mount Hagen. It's also widely available in the US. We enjoy Mount Hagen Organic Instant Caffeinated as well the DeCaffeinated versions. Of course fresh brewed organic coffee or espresso are also delicious and healthy.
Here's one link but there are many others regarding fiber in coffee -- just google it.
How about cold brewing instead of instant? It's less acidic, just as easy and quick to prepare, you only have to make it every 1-2 weeks, and you can use the best quality beans instead of the utter shite they use for instant. http://www.squidoo.com/cold_brew_coffee
It also makes a fantastic iced coffee mixed with some coconut milk. :-)
Health-wise, the dose makes the poison. It is a processed product. I do recall feeling funny when drinking it on an empty stomach. There may be use of nasty organic solvents in order for them to make it a powdery crystallized consistency. Why not just drink real coffee? The difference is 4 minutes.
I would re-iterate Knarf. In a choice of real vs processed, then I go for real every time I can. With a whole coffee bean, you get exactly what you see, a whole coffee bean. With a spoonful of freeze-dried granules, you can never be entirely sure what you are getting. If real coffee is not available though, I don't think instant coffee is going to do you that much harm...just not completely Paleo-ideal. If we were going there then I guess we'd chew on the leaves and eat the beans straight from roasting over our own open fire...
I'd be worried about fungal mycotoxins more than anything else.
AFAIK the most harmful component in baked goods (and particularly crisps, instant coffee, and substitute coffee products), is acrylamide which has caused a LOT of concern in the food industry.