In my experience I have found that aikido is usually misunderstood unless someone is participating.
My advice to everyone is, give it a go for a few sessions, if it is not for you then it is not for you. but at least you have had the experience.
The amount of exercise involved depends very much on the class. It can become very tiring especially for intermediate grades when they are wanting to put in more energy but put it in via muscle power and so tire out quickly. at the beggining I have found that it is not so exahusting because you are slower and just trying to become co ordinated. and at higher grades even though it can be tyring it is not as stenuous as you have learned to apply the energy in the correct way. I have an instructor who is extremely fit and so sometimes classes can be extrememly exhausting.
it all depends on the instructor (and what type of mood he is in)
2. we dont do TOO much weapons work.. again, go along and find out.
3. my mind already tended towards the spiritual before I started aikido. but, I have witnessed that people who practice aikido, even though they may not be aware of it gain a certain out look on life. It doesnt have to be looked at as spiritual, just a benificial way of looking at things. aikido can change you quite dramaticaly over large periods without you noticing.
4. As a martial art it cannot be studied alone, in my view. as it is all about the moment of intent between uke and nage. the foot movements and ukemi (falls) can be practiced alone. but the techniques are a little more tricky.
One of aikidos main benifits for me is that it is social, that it is about interaction. I wouldnt want to study it alone, I cant imagine it being half as fun.