In 1956, LEGO released 17 System i Leg sets across 3 subthemes, all of these sets have been retired. Subthemes for that year included HO 187 Vehicles, Supplemental, and Town Plan. For that year, the total price of all retail sets cost $36, today those sets are valued around $9,523.
Most valuable 1956 LEGO System i Leg set
700-0 Town Plan System $3,719.26
Highest growth 1956 System i Leg set
1310 ESSO Filling Station +93227.47%
Most owned 1956 System i Leg set
250-2 1:87 Esso Bedford Tanker
17 sets

224 2x2 & 2x4 Curved Bricks

Theme / Subtheme System i Leg / Supplemental
Year 1956
Pieces 14
Availability Retired
224 LEGO 2x2 & 2x4 Curved Bricks
Retail $0.50

231-2 Esso Pumps and Sign

Theme / Subtheme System i Leg / Supplemental
Year 1956
Pieces 2
Availability Retired
231-2 LEGO Esso Pumps and Sign
Retail $0.50
Value $140.60
Growth  +28020.0%
Annual growth 7.4%

236 Garage with Automatic Door

Theme / Subtheme System i Leg / Town Plan
Year 1956
Pieces 69
Availability Retired
236 LEGO Garage with Automatic Door
Retail $3.25
Value $374.94
Growth  +11436.6%
Annual growth 7.0%

250-2 1:87 Esso Bedford Tanker

Theme / Subtheme System i Leg / HO 1:87 Vehicles
Year 1956
Availability Retired
250-2 LEGO 1:87 Esso Bedford Tanker
Retail $1.15
Value $280.65
Growth  +24304.3%
Annual growth 8.2%

251-2 1:87 Esso Bedford Truck

Theme / Subtheme System i Leg / HO 1:87 Vehicles
Year 1956
Availability Retired
251-2 LEGO 1:87 Esso Bedford Truck
Retail $1.95
Value $259.30
Growth  +13197.4%
Annual growth 7.2%

252-2 1:87 Esso Bedford Trailer

Theme / Subtheme System i Leg / HO 1:87 Vehicles
Year 1956
Availability Retired
252-2 LEGO 1:87 Esso Bedford Trailer
Retail $0.70

275-2 1:87 VW Van

Theme / Subtheme System i Leg / HO 1:87 Vehicles
Year 1956
Availability Retired
275-2 LEGO 1:87 VW Van
Retail $0.70
Value $386.55
Growth  +55121.4%
Annual growth 8.9%

700-0 Town Plan System

Theme / Subtheme System i Leg / Town Plan
Year 1956
Pieces 264
Availability Retired
700-0 LEGO Town Plan System
Retail $12.50
Value $3,719.26
Growth  +29654.1%
Annual growth 8.5%

1200-2 Town Plan Board Small Plastic

Theme / Subtheme System i Leg / Town Plan
Year 1956
Pieces 1
Availability Retired
1200-2 LEGO Town Plan Board Small Plastic
Retail $4.00
Value $307.73
Growth  +7593.3%
Annual growth 6.4%

1226-2 6x8 & 2x8 Plates

Theme / Subtheme System i Leg / Supplemental
Year 1956
Pieces 4
Availability Retired
1226-2 LEGO 6x8 & 2x8 Plates
Retail $0.50

1227-2 4x8 & 2x8 Plates

Theme / Subtheme System i Leg / Supplemental
Year 1956
Pieces 5
Availability Retired
1227-2 LEGO 4x8 & 2x8 Plates
Retail $0.50

1228-2 4x8 Curved & 2x8 Plates

Theme / Subtheme System i Leg / Supplemental
Year 1956
Pieces 6
Availability Retired
1228-2 LEGO 4x8 Curved & 2x8 Plates
Retail $0.50

1231-2 Red Windows and Door with Glass

Theme / Subtheme System i Leg / Supplemental
Year 1956
Pieces 10
Availability Retired
1231-2 LEGO Red Windows and Door with Glass
Retail $1.00
Value $2.05
Growth  +105.0%
Annual growth 1.3%

1231-3 White Windows and Door with Glass

Theme / Subtheme System i Leg / Supplemental
Year 1956
Pieces 10
Availability Retired
1231-3 LEGO White Windows and Door with Glass
Retail $1.00
Value $2.05
Growth  +105.0%
Annual growth 1.2%

1270 5 Cyclists / Motorcyclists

Theme / Subtheme System i Leg / HO 1:87 Vehicles
Year 1956
Pieces 5
Availability Retired
1270 LEGO 5 Cyclists / Motorcyclists
Retail $2.00
Value $327.00
Growth  +16250.0%
Annual growth 7.6%

1271-2 Traffic Police Set

Theme / Subtheme System i Leg / Town Plan
Year 1956
Pieces 6
Availability Retired
1271-2 LEGO Traffic Police Set
Retail $1.25
Value $223.14
Growth  +17751.2%
Annual growth 7.7%

1310 ESSO Filling Station

Theme / Subtheme System i Leg / Town Plan
Year 1956
Pieces 96
Availability Retired
1310 LEGO ESSO Filling Station
Retail $3.75
Value $3,499.78
Growth  +93227.5%
Annual growth 10.3%