Putting aside any personal issues you may have such as children etc. the answer is that if you have the niche in the market for PQ’s then you will have a secure job, and from the employers’ viewpoint there is less chance that you will be looking for career progression, thus you may be a better bet as an employee.
You can, just as a qualified, keep up to date with all the changes in tax and accounting law, and thus your knowledge base will always be current. The application of accounting software is the same for PQs as for all others, so if you combine current know;edge with good software skills, there is no overriding need to return to studies. These may in fact be detrimental as they will give you technical knowledge which may detract from your practical approach.
Feel confident in your ability and unless you have an overbearing urge to return to studies, don’t be bullied into them.