I'm interested in wildlife photography, and have been considering upgrading to a better body from a Canon 450D, and get used to better features such as back button AF control. I have a limited budget, and I would like to save as much as I can for a long range telephoto lens. I have read some good articles about the Nikon 300 being a really good camera for wild life photography, and even other types of photography. I'm seriously considering purchasing the camera, but I'm concerned about the age of the camera, as the sensor technology maybe quite old (significant noise at higher ISOs than entry level DSLRs). Is the D300 still a good option in 2015 considering factors such as sensor noise?
I am not sure your question can be answered - it is a very subjective one, and what is worthy for you may well not be for someone else.
However, I have (over the last two years) bought a D300S and a second one as a backup camera. For me this camera has proved to be perfect - I mainly do landscapes. Although the size of images (at 12-15Mb) might be viewed as a disadvantage for this type of photography, I have found it not a problem in practice. The three main advantages of the camera for me are: the rear button AF; the 10 pin socket rather than the newer accessory connector used on the D7000 and like cameras; and its robustness. I had no end of trouble with the accessory sockets on my previous D90s - having to get a full refund for one camera as I could not get the D90/GP-1 combination to work at all even with multiple repairs and replacements of cables and connectors. Equally, the reason for buying the first D300S was that I managed to damage a D90 to the point that it was not economically worthwhile to repair the sheared off lens mount.
The main con for me is the weight of the machine, which is noticeably heavier than non-professional graded cameras. This I view as the cost of getting the benefits mentioned above.
The only recommendation I would make if going for a 300 is to go for the D300S rather than the D300. I am sure the articles you have read will give a list of differences between the two versions. When I came to look at the differences I found the change between the two greater than that of a minor upgrade, and well worth having. This does make a small difference in price - in UK terms the S seems to be currently about £50 more than the plain 300.