In 2013, LEGO released 5 Friends Summer sets, all of these sets have been retired. For that year, the total price of all retail sets cost $127, today those sets are valued around $224, a growth of 76%.
Most valuable 2013 LEGO Friends Summer set
41015 Dolphin Cruiser $140.00
5 sets

30108 Summer Picnic

Theme / Subtheme Friends / Summer
Year 2013
Pieces / Mini-doll figures 33 / 1
Availability Retired
30108 LEGO Friends Picnic
promotional
Value $4.00
Annual growth 1.6%

41000 Water Scooter Fun

Theme / Subtheme Friends / Summer
Year 2013
Pieces / Mini-doll figures 28 / 1
Availability Retired
41000 LEGO Friends Water Scooter Fun
Retail $6.99
Value $9.87
Growth  +41.2%
Annual growth 3.4%

41008 Heartlake City Pool

Theme / Subtheme Friends / Summer
Year 2013
Pieces / Mini-doll figures 423 / 2
Availability Retired
41008 LEGO Friends Heartlake City Pool
Retail $39.99
Value $55.60
Growth  +39.0%
Annual growth 2.6%

41010 Olivia's Beach Buggy

Theme / Subtheme Friends / Summer
Year 2013
Pieces / Mini-doll figures 94 / 1
Availability Retired
41010 LEGO Friends Olivia's Beach Buggy
Retail $9.99
Value $14.42
Growth  +44.3%
Annual growth 3.0%

41015 Dolphin Cruiser

Theme / Subtheme Friends / Summer
Year 2013
Pieces / Mini-doll figures 612 / 3
Availability Retired
41015 LEGO Friends Dolphin Cruiser
Retail $69.99
Value $140.00
Growth  +100.0%
Annual growth 7.7%