At some point I have had to allow particular users access to all records of several custom objects regardless of ownership, but I did not want to allow them to delete records.

I ended up using validation rules / apex code to prevent this.

Questions:

• Is it possible to restrict deletion but allow full access otherwise without the use of repetitive validation rules and / or triggers?
• By using sharing rules (or any other method), can I grant access to some users the ability to modify all, but only when meeting certain criteria (ex: reading and editing without requiring ownership for all Cases with Priority = 'High' and all other cases are hidden)