You are right, when you ghostwrite you take no credit and no one knows you were the mastermind behind the work.
I ghostwrite as a means to an end - financially.
It's worth it in that you earn a living and get paid up front as opposed to waiting for your own materials to sell. It's not something I recommend for long term or something I want to do forever.
The charge depends on the type of work you are doing.
My minimum charge:
General articles - $10+ per 500-1000 words
SEO articles - $20+ per 500 - 1000 words
Copy (sales page, web copy) $50-100 per 1000 words (depends on what client is willing to pay)
Fiction I charge between $20 - 40 per 1000 words. Repeat clients get discount depending on their budget. Sometimes the cost will be more depending on the client's budget.
The charge may differ from client to client.