Seward Park is a weird area of the lower east side. Many people who are not familiar with the city, feel as if it is too far from everything. This is a tricky area to invest in. You will likely be looking at $500K and upwards for a one bedroom in good condition, so if you were to get one for $300-$400K, it MAY make some sense.

The tricky part is that the normal time frame of 5-10 years for an expected positive return, will not be as accurate for this area. It is an underdeveloped area in terms of transportation, amenities and general services. Also, it has no real name recognition such as Murray Hill, Gramercy or even midtown or even the financial district for that matter. For the same budget, you would be better served looking for a condo in Washington Heights, L.I.C/Astoria or even Brooklyn. Even a studio in a brand new, high end luxury development makes more sense if in the right area of the city.

A co-op is more restrictive in terms of subletting, financials and also on the other side, most co-ops are older. People are enamored with new in this city right now, so I would think there are a lot of other options for this budget that are safer investment options over the long haul than Seward Park.
But I am just a real estate agent looking to help you, so what do I know ;-)