Total rider weight / load, how the bike is to be used (dual purpose vs tar only) and riding style would normally determine whether the fork and shock springs need to be upgraded for better handling.
The stock springs may do for a person with a weight of up to 120 - 150 lb but will eventually cause the shock to fail as the miles rack up. If your total weight (rider, passanger, luggage, farkels) exceeds this 150lb range, then it may be best to upgrade to springs that are more suitable for the extra weight or opt for the suitable aftermarket suspension upgrades available.
To me, a spring replacement will be cost less than trying to replace / repair a leaking / busted shock at a later date or buying an aftermarket replacement.
For a DIY rear spring replacement, have a look at
https://www.vstrom.info/Smf/index.php?topic=2195.0Also have a look at
https://racetech.com for info on springs