From Vapi either take a bus or train to Ahmedabad. From Ahmedabad either take a train or flight to Delhi.
From Delhi, depending upon the time of travel, you can choose one of these ways:
1. Delhi to Spiti via Shimla- This way is open throughout the year. You can choose either a cab or bus to Shimla first and then to Spiti.
2. Delhi to Spiti via Manali- This way is only open from July to September. If you are visiting Spiti during this period, you must take this route.
Happy travelling