4 plex on a double lot. Need some good advice....

[Glenn Tucker]

Looking at a 4plex that is in a great (A+) location.  All four units are small 1/1's that are dated but still in good condition.  The property is 2 blocks from the beach and has a solid rental history.  The numbers look like this.

Asking $415,000

Projected Purchase: 400,000

Down Payment: 100,000

Rent $785x4=$3140 month

Mortgage/Taxes/ins: $2551

Cashflow: 

COC return: 7%

Here is the kicker... It sits on a double lot that I could subdivide and add a duplex that would bring in an additional $2800 a month. 

Duplex: $200,000

Down Payment: 40,000

Rent: $2800

Mortgage/taxes/ins: 1523

Cashflow: $1277

COC return: 39%

All in Cash for both places: $140,000

COC Return: 14%

Looking for some advice.  I have only invested in sfr thus far.  This is a big jump for me and I could really use some unbiased thoughts.  Thank you... Glenn