If you're actively working to reach your career goals, then you understand "time" as the most valuable commodity. There are only so many hours in a day, of those hours you are mentally alert and focused a limited amount of that time. What you decide to give that time to should be strategic. You have family, friends and personal life to contend with while "working" on your career.
As for money, you're ensuring you attend the right networking events; some paid by the company and some paid by you. Do you ever wonder if it's worth it? Do you wake up the next day and wonder "Did I get anything out of this?"
If that is the wonder, then you've wasted both your time and money. You know you must weigh the value and cost when you spend money, but the silent currency is your time. Attending a networking event where you didn't:
connect with anyone with something outside of career (these are connections that you can keep throughout your career no matter where you are or what you're doing)
the speaker gave no information you can build on
the people were their own clique and you spent the evening as an outsider
who you need to know or their connections were not present
If none of those questions can be answered with a plus to you, then you wasted time and money. Money you can make back, but time wasted is gone.
Just something to think about as the weekend has come to an end.