There are a few things I did not see on the list that I learned in a volunteer management class.
It is important to understand what stage of life you are at and what your nature is. ie you might normally really love to work alone in a high powered way but you recently lost your husband and suddenly team work would be much more helpful in getting you back on your feet faster.
Sometimes highly professional people want to volunteer in an area outside of their area of expertise. Not only for their CV but to allow a part of them they never had time to cultivate a chance to flourish. Although this might not look like the most "effective" choice it might unleash a lot of passionate new inspiration and turn into something productive indeed.
The last point you made is so important It takes valuable staff time to orient a volunteer and manage them so you need to be really certain that your contribution warrants it. I find that even if I want to help an organization more directly as a volunteer, if they do not have a dedicated staff person that integrates volunteers then it can be quite frustrating for both sides. It is interesting to me that many orgs hire fundraisers. I would think it might be really useful to train fundraisers to be friend raisers for the organization as well and have them help integrate people into gratifying and meaningful volunteer positions.
Truly lovely post. Thanks