It really depends on the context. It could be quite sorrowful - a mother talking to her adult children who rarely visit her. It could be sarcastic, as you mention - perhaps between siblings who feel a family obligation is not being met. It's about context and delivery (how it is said) I hope this helps, Richard

It doesn't have to be sarcastic, but you would have to be very careful in your tone of voice so it's not interpreted as such. If you didn't want to be sarcastic, you would usually use 'sometime', not 'sometimes' and say: "It would be nice to see you sometime". This could also be interpreted as sarcasm if the wrong tone of voice is used, but it's still a safer bet than your first option. Even safer (from being interpreted as being sarcastic), you would use 'sometime' and terminate the sentence with a word like 'soon'. "It would be nice to see you sometime soon".